All good things must come to an end. At least that's likely the case for T-Mobile USA customers who like using the carrier's Wi-Fi calling feature on certain smartphones.

In this week's column, I discuss whether I think AT&T will keep the Unlicensed Mobile Access Wi-Fi calling feature that T-Mobile offers on some of its smartphones. I also discuss Samsung's problem with long delays for Android OS updates. And I explain to a Boost Mobile customer that he has two years to pick out a new phone before Sprint turns out the lights on the existing iDEN network that the Boost service currently uses.

Ask Maggie is a weekly advice column that answers readers' wireless and broadband questions. If you've got a question, please send me an e-mail at maggie dot reardon at cbs dot com. And please put "Ask Maggie" in the subject header.

Dear Maggie, UMA, or Unlicensed Mobile Access, Wi-Fi calling is a terrific (and often misunderstood) feature on some T-Mobile phones. It's one of the reasons I'm a T-Mobile customer, because it's something no other carrier offers. Will AT&T continue to support this feature after it buys T-Mobile UMA is especially valuable overseas, because calls to U.S. numbers don't incur international roaming charges. They just use plan minutes.

Thanks, Russ

Dear Russ, I contacted AT&T spokesman Mark Siegel to get an answer to your question, and once again he told me that it's just too soon to say exactly what phones, service plans, or features AT&T will keep or kibosh after it buys T-Mobile USA.

The merger still has a long way to go in terms of getting approved. When the deal was announced last month, the companies said they expected the regulatory review process to take at least a year.

"Until this deal is closed, we remain an independent competitor to AT&T," a T-Mobile representative said in an email. "There is no change in service for our customers, and we remain committed to ensuring that our customers have the best experience possible using T-Mobile USA products and services, and that includes offering Wi-Fi Calling on T-Mobile smartphones."

As for UMA being a cool feature, I think you're right. This feature, which T-Mobile began testing in 2006, has been available on some BlackBerry devices, such as the Curve 8520, Curve 3G, and Bold 9700 and the Nokai E73 exclusively on T-Mobile's network. And it looked like up until last year, T-Mobile was expanding the device lineup for the feature. In November, it announced it would offer UMA-based Wi-Fi calling on some Android smartphones via an Android App. But the feature is not available for every Android phone.

T-Mobile initially made the app available for the myTouch and Motorola DEFY. Since then, T-Mobile has added or launched Wi-Fi Calling on the Samsung Vibrant, Galaxy S 4G, Sidekick 4G, plus the Motorola Charm and Cliq2, along with the T-Mobile G2x and the MyTouch 3G Slide, according to Steve Shaw, vice president of Kineto Wireless, the company that provides the Wi-Fi calling functionality for T-Mobile. For a full list of devices, including Nokia and RIM phones, click here.

Shaw said that about 80 percent of T-Mobile's smartphone line-up has Wi-Fi calling, and he estimates that nearly 20 percent of T-Mobile's total subscriber base has a Wi-Fi Calling enabled phone.

The UMA-Wi-Fi calling feature is integrated into the BlackBerry and Nokia phones, making it a seamless experience. Calls can be routed on and off the Wi-Fi network. But the Android app-based version isn't integrated into the device. So it doesn't switch between Wi-Fi and the cellular network as seamlessly as the native versions on the BlackBerry phones and the Nokia device.

T-Mobile has changed the service a bit since it first began offering it a few years ago. Previously, T-Mobile charged $10 extra per month for unlimited voice minutes when your call was handled over a Wi-Fi network. Now T-Mobile doesn't charge people extra for the service, and calls routed over the Wi-Fi network are still counted against your monthly voice minutes. But the UMA Wi-Fi functionality allows you to make calls when a cellular signal isn't available.

So as you mentioned in your question, it's a very nice feature to have while traveling overseas, because you can use the Wi-Fi connection to make phone calls as though you were on T-Mobile's U.S. network, avoiding expensive roaming charges.

Unfortunately, I doubt AT&T will continue selling phones with the UMA feature, and I doubt the company will continue to support devices from T-Mobile that have that feature after customer contracts expire. T-Mobile uses the UMA feature mainly because it lacks good network coverage. By contrast, AT&T doesn't need Wi-Fi to fill in for dead spots for its voice service. The company has a robust national network footrpint. Customers who experience dropped calls aren't experiencing those dropped calls because the cell phone signal is weak. They are experiencing issues because the networks are overloaded. Once AT&T acquires the T-Mobile spectrum, it will have a lot more cellular capacity to go along with its coverage.

That said, AT&T does see Wi-Fi as a useful offloading technology for data services. Through roaming arrangements, AT&T customers have access to more than 135,000 Wi-Fi hot spots around the globe, and T-Mobile customers can access an additional 45,000 Wi-Fi hot spots globally. AT&T currently offers smartphone customers in the U.S. the ability to connect at no additional cost to its hot spots for data services. This helps offload traffic on AT&T's congested 3G data network.

But I wouldn't hold my breath for Wi-Fi based voice calling. AT&T seems to view Wi-Fi purely as a data offload network technology.

Kineto's Shaw disagrees with me. He thinks that AT&T could leverage its existing broadband business to offload voice traffic onto Wi-Fi.

"The most interesting opportunity for Wi-Fi Calling is AT&T's 16 million DSL and U-Verse lines the company has into consumers' homes," he said. "Approximately 80 percent of those lines already have Wi-Fi. And nearly every analyst out there tells us anywhere from 50 percent to 66 percent of mobile usage happens indoors, particularly in the home."

Shaw makes a great point, but given the fact that AT&T has not included UMA Wi-Fi calling on its phones already, makes me think the company probably isn't that interested in leveraging in-home Wi-Fi to offload voice calls.

Correction and Update 4:45 p.m. PT:T-Mobile USA offers the UMA Wi-Fi calling feature on several more Android phones. The story incorrectly listed that the feature was limited to two phones. The story was also updated with a comment from T-Mobile USA and comments from Kineto Wireless, the company that supplies T-Mobile with the UMA capability.

Hi Maggie, I have the Samsung Fascinate from Verizon Wireless and have been waiting for an upgrade to Android 2.2 ever since I got the phone. When I got the phone in November, the Verizon employee at the store assured me an update would happen. But it still hasn't come. Meanwhile, other Samsung Galaxy S phones have all been updated. And now the Galaxy S2 phones are coming out with Android 2.3. Do I have any hope of ever getting the Android 2.2 update on my phone Or have Samsung and Verizon chosen to neglect this phone

Thanks for your help, Emory

Dear Emory, I hear your frustration and you are not alone. This has been an ongoing problem since the Galaxy S phones were first introduced last year. I contacted Samsung and asked them to answer your question. The company claims the holdup has to do with testing the software and the device to make sure the user experience is up to snuff.

Here is the reply I received:

But delayed software upgrades have been an issue with Samsung Android phones for a while. My CNET Reviews colleague Bonnie Cha noted in a blog post in January that several Galaxy series devices have been on the market more than seven months without the promised update to Android 2.2.

Meanwhile other handsets from other manufacturers, such as the Motorola Droid X and HTC Evo 4G, have received the Android 2.2 update.

It's difficult to say for sure why it's taking Samsung so long to get these upgrades ready for its phones. Bonnie suspects it has something to do with Samsung's user interface. Samsung had also been criticized for not pushing updates to the Samsung Behold II after Android OS 1.6.

"Though the company never officially said it, we suspected the TouchWiz interface was to blame, which is why we were concerned when we saw an even more customized TouchWiz UI on the Galaxy phones," Bonnie said in her post in January. "But at the time, Samsung assured us updates would not be a problem."

Other people have come up with conspiracy theories to explain Samsung's slow movement in the update department. In January rumors were flying around that Samsung was actually preventing T-Mobile from releasing the Android 2.2 Froyo update to the Samsung Vibrant, so that the company could push customers to upgrade to the next-gen Vibrant 4G.

At the time, Samsung wouldn't comment on the rumor, but it issued this statement:

My colleague Bonnie said it best in her blog: "We appreciate the thoroughness in testing, but this doesn't help Samsung's cause. I really hope for its sake that all Galaxy owners get a helping of Froyo soon." Amen, Bonnie.

Dear Maggie, I've been a Boost Mobile customer for a while and like the service. I understand that Sprint is going to shut down the Nextel iDEN network in 2013 that my Motorola i1 uses. Do you know what the game plan is for customers on the Nextel network, or have you heard anything I'm thinking Sprint may move the users over to their network, or do I have to wait and see I'd like to hold on to my Motorola i1 for as long as I can because I love the phone. But I understand that I will probably need to upgrade. Keep up the good work.

Thanks, Bill

Dear Bill, You're correct. Sprint announced that it will migrate users away from the old iDEN network that Nextel used and toward Sprint's CDMA network. Sprint will repurpose the spectrum and eventually switch off the iDEN cell sites. And since Boost uses Sprint's iDEN network to deliver its service, this means that eventually your Motorola i1 will no longer work.

The good news is that Sprint plans to retain the basic elements of the push-to-talk (PTT) service that Nextel offered and that you probably like having on your Motorla i1. But instead of being offered over an iDEN network it will be offered on Sprint's CDMA network. John Taylor, a spokesman for Sprint, said that this will allow people to not only take advantage of the push-to-talk feature but also get access to faster data service from Sprint's 3G EV-DO network. It should also improve in-building coverage and extend the geographic network coverage in general.

Sprint will begin this transition process from iDEN to CDMA by the fourth quarter of this year. But the company has said it will keep the iDEN cell sites operating until 2013.

What this means for you is that you'll have some time to pick out a new phone. In fact, you'll have about two years.

In the short term, Sprint will be rolling out new CDMA devices with Direct Connect, the push-to-talk functionality, to attract new customers and encourage existing iDEN users to transition to the CDMA. So you'll likely be able to upgrade your phone before 2013, to a CDMA push-to-talk version, if you see a new phone that strikes your fancy.

Sprint has said these devices will initially come from Kyocera and Motorola. My CNET Reviews colleague Kent German reported last month when Sprint made its road map public that exact details about the new devices are still few. But he said the first crop of Sprint phones "should include a durable flip phone with a digital camera and an Android-powered smartphone with a touch screen and a full QWERTY keyboard." He also said Sprint promises more CDMA push-to-talk devices with varying designs in 2012.

I can't say for certain that the same lineup of phones will be available for Boost Mobile, but it's likely Boost will include a device that's very similar to your Motorola i1 that will work on the CDMA network.