I am considering the purchase of the MacBook Air (AAPL). If this computer freezes up, as my current Dell Inspiron does on occasion, how would I correct for that? I usually remove and then replace the battery on the Dell (DELL). But what would I do if this happens with the Air, since it has no removable battery?

You can force a frozen MacBook Air — or any current Mac laptop — to shut down and restart without removing its battery. You just hold down the power button for a few seconds until the machine shuts off, then wait a few seconds, then turn it on again.

I am a Verizon (VZ) customer and have a Palm (PALM) Treo 700W for personal use. I would like to replace the Treo but, in light of Verizon’s announced “open network” policy, I am wondering if this is the right time.

It’s far too early to know what new phones will be available under the new Verizon program, since that depends on which phone makers decide to make devices to run on the “open” network, and what kinds of devices they might produce. There is the potential for phones that are more creative or interesting than what is available today, but it’s only a potential. Verizon has just laid out the first details of the plan, and no product announcements are likely for quite a while. If your Treo needs replacing soon, and you want to remain a Verizon customer, you will have to choose from the company’s current smart-phone offerings.

Are there any cellphones that allow for two separate phone numbers? Right now I carry two devices, both with the same carrier.

At least in the U.S., each cellphone, or each SIM card that goes in a phone, is normally tied to a single number. To use two numbers on a single phone, you could purchase an unlocked phone running on a GSM network and then purchase two SIM cards, each with a separate number, and swap them in and out. But that would be an inconvenient process, since inserting and removing SIM cards typically requires opening the phone and even removing the battery.

You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.

When will Google offer its much-discussed cellphone for sale?

Google says it isn’t planning to build or sell mobile phones. Instead, it is developing a cellphone operating system, or software platform, called Android. And it has assembled an alliance of companies, including phone makers and cellular network providers, to create phones based on this new platform. This group is called the Open Handset Alliance. In addition, since Android will be so-called “open source” software, Google expects numerous developers around the world, large and small, to modify the operating system and create programs that will run on it.

If all goes according to plan, Google says it expects to see many different Android-based cellphones and other mobile devices, from a variety of manufacturers and carriers, in various designs and with differing functionality and capabilities. Some may be larger-screen “smart phones,” similar to an iPhone or BlackBerry. Others might be smaller, simpler phones. Still others might fall somewhere between an iPhone and a small laptop.

Google officials say they expect the first Android devices to be available later this year.

After reading your Jan. 3 column, I looked unsuccessfully for a Home and Student version of Office for Mac 2004. Does such a version exist?

In the 2004 release of Microsoft Office for the Mac, this low-priced version had a different name: the Student and Teacher edition. Microsoft presumably changed the name of this $150 product to the Home and Student edition in both Office 2007 for Windows and Office 2008 for the Mac, because, while it was technically limited for sale to families containing students or teachers, no proof was required and it was widely purchased by consumers in general.

However, there’s a big difference between the latest Windows and Mac versions of the Home and Student edition. In the Mac version, it includes Word, Excel, PowerPoint and Entourage, Microsoft’s equivalent of Outlook on the Mac, which, like Outlook, includes email, calendar and contact functions. But the new Windows version now omits Outlook, and instead substitutes OneNote, a note-taking and information organizing program that is far less commonly used. So, Windows users must spend much more money to get a version of Office that includes Word, Excel, PowerPoint and Outlook.

Is there a way to back up Microsoft Outlook Express emails, particularly Inbox items?

Outlook Express stores your emails in database files, with all the messages in each of your mail folders lumped into a single such file. These files can be backed up, or copied, onto other hard disks, or storage media.

The email data files are usually buried in obscure subfolders in Windows. But you can locate them by clicking on the Tools menu, then Options. This will open a tabbed window. In this window, click on the tab called Maintenance, then the button called Store Folder. This will generally give you a long, complicated path to the folder.

Next, copy this path by selecting it and pressing Control and C. Then, click on the Start menu, select “Run…”, and then press Control and V and then click OK. This should open the folder that contains your email. The inbox is contained in a file called Inbox.dbx. This is the file you will want to back up. If you want to back up other folders, such as the Sent mail folder, you will find them along with the inbox file, with the same “.dbx” suffix.

Some backup programs may automate this process by simply allowing you to designate that you want to back up your Outlook Express emails. There are even some programs specially designed to back up Outlook Express messages. You can find some of these by simply performing a Web search on “backup Outlook Express.”

• You can find Mossberg’s Mailbox, and my other columns, online for free at the new All Things Digital Web site, http://walt.allthingsd.com.

Q. Is there any way to watch high-definition TV on a Mac in real time — not downloaded from a service?

A. As on Windows computers, there are add-on TV tuners for Macs that can both receive and record TV programs in real time. Some of them can handle high-definition programming. The best-known company that sells such tuners for the Mac is called Elgato, at elgato.com.

Q. I’m interested in your perception of the Treo’s future. I currently use (and generally like) a Treo 650. I’d like to upgrade, but I’ve read recently that Palm’s future is uncertain. I wonder if you think the Treo is on a slippery slope down, while the Apple iPhone will likely improve.

A. I do believe that Palm has allowed its software to stagnate and hasn’t moved fast enough to make its hardware thinner and cheaper. However, there are also some positive signs at Palm. Its new Centro phone is pretty good, smaller and less costly than a Treo. And the company is receiving an influx of funds and talent from a group of outside investors with experience at Apple, among other places.

Palm’s fate and future may depend on the success of a project it has undertaken to create an entirely new operating system. But the outcome of that effort won’t be known for quite some time.

The iPhone, which is already very good, will likely get better, as it is just at the beginning of its life. It has raised the bar for other smart-phone makers, such as Palm, especially when it comes to software. But I expect other companies to match at least some of the iPhone’s features and style, which means Apple will have to hustle to keep its lead. In the past five years, Apple has done very well at staying ahead of competitors in the design of its computers and portable music players. But the cellphone business is full of companies with more imagination than the typical PC maker and more resources than many makers of portable music players, so the challenge for Apple will be greater.

Q. My mom is legally blind and has difficulty working with email and downloading files. I try to help her by phone, but it never works, and we live far apart, so I can’t just go over to help her. I would like to install an application on her PC where I can take over remotely from home. Do you have any suggestions for this type of application?

A. There are a number of possibilities. One very simple option is a program called CrossLoop, at crossloop.com. Some versions of Windows, such as Windows XP Professional and Windows Vista Ultimate, also have remote desktop control built in.

You can find Mossberg’s Mailbox, and my other columns, online for free at the new All Things Digital Web site, http://walt.allthingsd.com.

Write to Walter S. Mossberg at mossberg@wsj.com

On two different new computers, I’ve created Word files and they’re automatically saved with the extension “.docx.” What is that? When I send these files via email, no one can open them. Can you shed some light?

In the 2007 version of Microsoft Office for Windows, which you appear to have on your two new PCs, Microsoft introduced new default file formats whose extensions end in the letter “x”. The one for Word is “docx,” for Excel it’s “xlsx” and for PowerPoint it’s “pptx.” You are using Word 2007, and all of your files are thus automatically being saved in the “docx” format.

Your correspondents can’t open these files because they are using older versions of Office that don’t recognize the new formats. Microsoft has made available a free auto-conversion patch for the older Windows Office versions, but most people don’t have this patch. (It can be found at microsoft.com/downloads under “Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats.”)

There’s also a kludgy free stand-alone converter from Microsoft for the Mac versions of Word and PowerPoint, available at microsoft.com/mac under the name “Microsoft Office Open XML File Format Converter for Mac.”

Unless you can persuade all of your correspondents to install these workarounds, I suggest you change a setting in Word 2007 so that, henceforth, all of your files will be saved in the traditional “doc” format. That familiar format isn’t only compatible with older versions of Microsoft Office, but with many other programs, on both Windows and the Macintosh.

To make the change, first click on the round “Office Button” at the top left of Word 2007. Then, at the lower right of the window that appears, click on “Word Options.” In the next screen that comes up, click on “Save” in the column at the left. In the panel that appears at the right, you’ll notice an option called “Save Files in this format,” with a drop-down list of choices next to it. Display the list of choices by clicking on the arrow and select “Word 97-2003 Document (*.doc)”. Then, click OK at the bottom of the window.

Microsoft warns that some new features in Word 2007 won’t translate into the old format, but I believe that this will prove irrelevant in 99% of cases and is outweighed in any case by the incompatibility you have run into.

How can I transfer all my Outlook contacts from a Windows PC to a Macintosh contacts program?

There are a number of methods. You can use a PDA or smart phone that can synchronize the contacts with a Mac, after having first synchronized with Outlook on your PC. Or you can use a $10 program called O2M, which is specifically designed to move Outlook data to a variety of Mac programs. It can be downloaded at littlemachines.com.

Or you could get Apple to do it. The company offers a basic file transfer for free if you buy the Mac from an Apple retail store. But, if you want Apple to move Outlook contacts in just the way you want, you may have to purchase the company’s $99 a year ProCare service, which comes with a more complete transfer service.

I recently replaced an old Windows XP computer that was running very slowly. I want to continue to use it as the computer for our young kids, and I was thinking that if I format the hard drive and reinstall XP (which I bought to upgrade the machine a while back), it will probably improve its performance. Do you agree? And, can I reinstall my copy of XP, when I have already “activated” the software when I originally installed it?

I do agree that the computer will likely run faster after you wipe the hard drive and reinstall Windows. That is the usual outcome. And it should be possible to use it legally, as long as you haven’t made any major changes to the hardware, since Microsoft’s activation system typically allows Windows to be reinstalled on the same machine. If activation fails, you can call Microsoft and explain that it’s the same machine, and the company says it will usually OK activation in such cases.

You can find Mossberg’s Mailbox, and my other columns, online for free at the new All Things Digital Web site, http://walt.allthingsd.com.

Write to Walter S. Mossberg at mossberg@wsj.com

This week, I was swamped with questions about Apple’s hot new iPhone, so this is a special all-iPhone edition of Mossberg’s Mailbox.

Can you physically remove the included AT&T SIM card from the iPhone and replace it with another AT&T card or one from another wireless carrier?

Yes, and no. The SIM card, which carries the iPhone’s account information, can be removed by inserting a paper clip into a tiny hole at the top of the phone. However, Apple says that if you replace the included card with one from another carrier, like T-Mobile in the U.S., or Orange in Europe, the phone won’t work. According to Apple, some non-iPhone AT&T cards may work, but some may not.

It’s possible that hackers will figure out a way to override this lock on other carriers’ SIM cards. But, as of now, the iPhone will work only with AT&T. Even overseas, at least until Apple does deals with foreign partners, you won’t be able to use SIM cards from other carriers. The iPhone will work overseas, but you will have to roam with AT&T and pay high charges. For instance, according to an AT&T spokesman, if you make a call in Europe, it would cost $1.29 a minute. It would cost 99 cents a minute if you are on one of AT&T’s $5.99 per month international plans.

Since the iPhone battery is sealed in and can’t be easily replaced by the user, what happens when it dies? Will you have to buy a new iPhone?

No, but you will have to send the phone to Apple, or drop it off at an Apple store, to have the battery replaced. The battery is covered during the phone’s one-year warranty period. After that, replacing the battery costs $79, plus $6.95 for shipping, and takes three business days. Details are at apple.com/support/iphone/service/battery/. Some small companies may eventually offer to do this for less, or in less time, as they have for the iPod.

One twist: because a phone is a necessity, Apple is offering loaner iPhones for $29 while your phone’s battery is being replaced, or for the period of any other repair on the iPhone. You will have to switch the AT&T SIM card from your own phone to the loaner, and then back again. Details are at apple.com/support/iphone/service/faq.

In addition, Apple warns that all the data on your iPhone will be wiped out during a battery replacement, but notes that it can easily be restored by simply syncing again with the iTunes software on your computer once you get it back with a fresh battery. That’s because, whenever you sync your iPhone with iTunes, it backs up the data on the phone. You can also use this method to fill your loaner iPhone with your own data.

Can I use the iPhone via a Bluetooth wireless connection in my car? Can I use Bluetooth to transfer files or other information between the iPhone and a computer?

In my two-week test of the iPhone, I succeeded in connecting it without much trouble to the built-in audio system and microphone on a friend’s BMW. Almost instantly, the over 700 contacts I had on my test iPhone were displayed on the car’s dashboard screen and calls could be made and received through the iPhone.

However, this first iPhone can use Bluetooth to connect only with cars and with wireless phone headsets. It cannot use Bluetooth to transfer any data to or from a computer, to play music through stereo wireless headsets, or for any other purpose. As with many other missing features, Apple has the ability to add these to the iPhone through software updates delivered by synchronizing with your computer.

If the iPhone’s Web browser is so good, why can’t it play video on Web sites I visit?

At launch, the iPhone version of the Safari browser is missing some plug-ins needed for playing common types of Web videos. The most important of these is the plug-in for Adobe’s Flash technology. Apple says it plans to add that plug-in through an early software update, which I am guessing will occur within the next couple of months. However, a separate program included on the iPhone can play a limited selection of videos from YouTube, and the phone can play videos you purchase from Apple’s iTunes store, and certain videos you create yourself.

You have been critical in the past of some smartphones that don’t allow you to delete emails with a single click. Can the iPhone do this?

Yes. If you are reading an email and want to delete it, you just tap on a trash can icon at the bottom of the screen and the message disappears into the trash can with an animation that resembles water being poured through a funnel.

However, in the iPhone email program’s list view, it takes two steps to delete an email. You have to swipe across the message header or preview with your finger, and then tap the red delete button that appears. You can also press an “Edit” button, which allows you to delete emails in the list view, but this still requires two taps per message.

Unlike on a BlackBerry or Treo, the iPhone doesn’t allow you to delete whole groups of email en masse by date, or even to select large groups and then delete them en masse. This would be a good feature for Apple to add down the line.

Can you buy an iPhone and just use it to play music and videos like an iPod, and to surf the Web or get email over Wi-Fi, without signing up for an AT&T service contract?

No. None of the iPhone’s functions, except calling 911, will work unless the phone is covered by a two-year AT&T service contract, and has been “activated” by AT&T. That will cost you $60 a month at a minimum. If you are thinking of buying an iPhone, you should plan on being an AT&T customer, and if AT&T coverage is poor where you live, work and travel frequently, I advise you NOT to buy an iPhone.

You and many others have criticized AT&T’s EDGE data network, which the iPhone uses, as slow. You have noted that AT&T has a much faster data network. Can the iPhone be upgraded to use that faster network?

No, it can’t. This first edition of the iPhone can’t use any cellular network faster than EDGE, which is much, much slower than the fastest cellphone data networks available from AT&T, Verizon or Sprint. It can, however, use very fast Wi-Fi wireless networks, when you are in range of them.

Apple hasn’t said anything about future iPhone models, but I fully expect a future model that can use these faster cellular networks, which are usually called 3G networks. So, if this is very important to you, I’d suggest waiting to see if such an iPhone emerges. But I don’t expect this to happen anytime soon.

In the past few days, AT&T seems to have tweaked its EDGE network, at least in some locations, so it runs faster than it has in the past. In my own speed tests, around Washington, D.C., I have seen repeated speeds of around 150 kilobits per second, roughly 50% better than the 100 kbps I have seen with EDGE in the past. However, I have also recorded speeds as slow as 82 kbps. And, even the new, faster speeds are way below those of the faster American cellular data networks, which can easily reach 500 to 800 kbps on a phone.

How good is the iPhone’s To-Do list or Task function?

Awful — in the sense that it doesn’t exist. The phone does have a calendar, of course, which syncs with the most popular calendar programs on Windows and Macintosh computers. And it has a Notepad, which doesn’t sync with any program on any computer (though you can email notes to yourself and others). But it has no To-Do list function at all.

Write to Walter S. Mossberg at mossberg@wsj.com

Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability. This week my mailbox contained questions about browsers’ antivirus capabilities, smartphone memory, Wi-Fi router speeds and the limits of burning songs from iTunes.

If you have a question, send it to me at mossberg@wsj.com, and I may select it to be answered here in Mossberg’s Mailbox.

Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

Does the Firefox browser that you recommend contain antivirus capabilities?

No. I know of no Web browser that includes the ability to block, detect or remove viruses. For that, you need separate antivirus software, which every Windows user should obtain and keep updated. You should also run a strong firewall program and an antispyware program.

Firefox does omit some of the features in Microsoft’s Internet Explorer browser that digital criminals have misused to place malicious software on computers. This doesn’t mean that Firefox is perfectly safe. As it has become more popular, some vulnerabilities in the new browser have been uncovered, and it’s likely that digital criminals will get better at exploiting these vulnerabilities. Still, on balance, Firefox is more secure than Internet Explorer.

I am thinking about upgrading to the new Treo 650 smartphone from PalmOne. But I would like to know if the company ever fixed the memory problem you wrote about with the initial Treo 650 units?

Yes. Sprint, the cellphone carrier that launched the Treo 650, has — just this week — issued a patch from PalmOne that supposedly remedies the memory problem. I haven’t tested it, so I can’t say if it works.

The memory problem, which mainly affected power users, didn’t impair the basic functionality of the phone. But it caused databases, like address books and digital dictionaries and maps, to take up more room on the 650 than the same files had occupied on the earlier Treo 600 model. The patch issued this week revises the way the 650 manages memory so these large files take up less memory. It may not restore the full efficiency of the older memory system, but it should ease the problem significantly.

I just signed up for DSL broadband service with a maximum speed of 1.5 megabits per second. Which type of Wi-Fi wireless router should I buy in order to handle the maximum speed — the “b” type or the “g” type?

Either type has enough capacity to handle the top speed of your new service. The “b” routers top out at 11 megabits per second, and the “g” models can go up to 54 megabits per second, though they drop back to the speed of “b” if you have any “b” equipment on the wireless network.

If I buy songs from the iTunes Music Store, or one of its competitors, can I record these songs to blank CDs in order to make music CDs that can be played in my home CD player?

Yes. Song files purchased from iTunes and other legal download sites can be recorded, or “burned,” to CD an unlimited number of times. And, they can be combined with any other songs, either those you purchase or those you create from your own commercial CDs. These CDs you burn can be played on most home, auto and portable CD players. The only limitation is that you can’t burn the exact same collection of songs, in the exact same order, to CD more than seven times.

* * *

Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

Write to Walter S. Mossberg at mossberg@wsj.com