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Would a T-Mobile iPhone play nicely on AT&T? (Ask Maggie)

CNET's Maggie Reardon explains how a T-Mobile iPhone, if one arrives later this year, would work in the wake of the planned AT&T merger. Plus: the future of Sprint's unlimited data plan.

Rumor has it that Apple is planning to sell its latest crop of iPhones not just to AT&T and Verizon Wireless customers, but also to Sprint Nextel and possibly T-Mobile USA customers.

This is great news for millions of customers who have remained loyal to these smaller operators. But some consumers are wary about buying a new iPhone from T-Mobile when the company is expected to be purchased by AT&T early next year. Will a T-Mobile iPhone even work on the AT&T network? I answer this very question in the column below.

Also in this week's Ask Maggie, I explain what I think current Sprint customers might expect if the company ditches its unlimited data plan. And I offer some advice whether to install antivirus software on a smartphone.

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.

Covering your iPhone bases

Dear Maggie,
I am a T-Mobile customer, and I'd really like an iPhone. So I was very happy when I read that T-Mobile might get the iPhone 5 this fall. But I have a question. If I get the iPhone on T-Mobile and AT&T buys T-Mobile will my iPhone work on AT&T's network? Or will I have to buy a new AT&T iPhone anyway? I know that using an unlocked AT&T iPhone on T-Mobile means you can't get 3G service. Just wondering if there are any limitations going the other way?


Dear Travis,
The short answer to your question is: Yes, you will be able to use the T-Mobile iPhone, on AT&T's network after the merger. (Before we get too much further, let me say that I don't know for certain that a T-Mobile iPhone will be introduced. That's the latest rumor. So the answer to this question is purely hypothetical.)

AT&T and T-Mobile USA use the same basic cellular phone technology known as GSM, or Global System for Mobile Communications. And their advanced 3G technologies are the same as well, HSPA and HSPA+. Most of the world uses this GSM technology, and it's this commonality that allows you to swap SIM cards in and out of unlocked phones so they can be used on different networks around the world.

By contrast Verizon Wireless and Sprint Nextel have based their networks on CDMA technology. And their 3G networks use what's called EV-DO.

One of the reasons that AT&T is buying T-Mobile is because of these network synergies. The network equipment and the devices that use this network can be interchangeable, so it will make the integration of the networks much easier down the road when the merger is completed.

But as you point out in your question, even though the underlying technology is the same, an unlocked iPhone from AT&T can't get access to T-Mobile's 3G network. But as I stated earlier, assuming Apple releases an iPhone for T-Mobile's network, an unlocked T-Mobile iPhone will be able to access AT&T's 3G network.

Here's why: T-Mobile users two sets of spectrum for its 2G and 3G services. The 850MHz and 1900MHz spectrum is used for 2G service. And the 1700MHz and 2100MHz spectrum frequencies are used for the 3G HSPA and HSPA+ service. Meanwhile, AT&T uses the same set of spectrum for both 2G and 3G and it happens to be the 850MHz and 1900MHz spectrum frequencies that T-Mobile uses for 2G.

So if Apple builds an iPhone for T-Mobile, it must include all the frequencies that T-Mobile supports on its network to ensure that consumers get maximum coverage. And since T-Mobile uses the 850MHz and 1900MHz spectrum for its 2G service, it will be baked into the phone along with the 3G frequency so it can support 3G service. And since those are the same frequencies that AT&T uses for its 3G service, the phone should work on AT&T's 3G network as well as T-Mobile's 3G network.

Here's a cheat of the spectrum bands supported:


  • 850MHz = 2G
  • 1900 MHz = 2G
  • 1700MHz/2100MHz =3G


  • 850MHz = 2G/3G
  • 1900MHz = 2G/3G

So the bottom line for you is that if T-Mobile ends up getting its own version of the iPhone, you should be good to go even after AT&T acquires the company. You could keep the same phone and theoretically have access to both networks.

But keep in mind that after AT&T takes over T-Mobile, which is expected in the early half of next year, there are still lots of things that must be done to integrate the networks. So your T-Mobile iPhone will not be running on AT&T's network right away anyway. But as the companies merge their networks, you won't have to worry about your iPhone being incompatible with AT&T's network. By the way, this is true of any 3G smartphone on T-Mobile's wireless network.

The future of Sprint's unlimited data plan

Dear Maggie,
I've been with Sprint on a family plan for a little over a year and I have the unlimited data plan. I've been considering switching to Verizon for a few months, because it has better service in my area right now than Sprint. But I don't want to give up my unlimited data plan. I've read that at some point Sprint is going to have to give up unlimited data and give in to tiered data plans. If they do this do you think I will still be able to continue with my unlimited plan as Verizon and AT&T customers have been able to do?


Dear bsears2007,
As I've said several times before in this column, I don't think that most people need an unlimited data plan. So I wouldn't recommend choosing a carrier solely based on that. Instead, I'd suggest that you choose the carrier with the best coverage and service in your area. Because if you can't access the network, it won't matter how many voice minutes or megabytes of data you can use in a month, you won't be using your phone at all.

That said, I understand that people are attached to their unlimited data plans and they don't want to let them go. If that is the case with you, then I'd just hang on to your Sprint plan. There's a good chance that Sprint will get rid of its unlimited data plan, as my colleague Roger Cheng has written, especially if rumors are true and it gets the new iPhone this fall.

And for as long as you are under contract, you will still get that unlimited data plan. After that, it's hard to say what Sprint will do with its unlimited data service for current customers. My guess is that it won't want to spook its current customer base and send them packing for AT&T and Verizon. So I would expect that the company would grandfather in current customers and allow them to keep their unlimited data plans just as AT&T and Verizon have done.

But at the same time, the reason that Sprint will likely move toward tiered pricing is because it is now attracting data hogs fleeing AT&T and Verizon. On average Sprint customers consume almost twice as much data as AT&T and Verizon customers. And usage has been growing on its network. So Sprint may have to do something to curb current users' data usage.

One thing the company may consider is throttling heavy users. T-Mobile already does this for its data customers. And AT&T recently said it would throttle or slowdown service for grandfathered unlimited data customers who consume more than 2GB a month. The idea is that AT&T wants to limit usage of the small percentage of customers using a disproportionately high amount of data.

I guess we'll just have to wait and see. If you aren't under a contract now, it might be a good time to sign up for one. That way you can lock in your unlimited plan at least until the end of your contract.

I hope that helps and good luck!

Securing Android

Dear Maggie,
I've been reading quite a bit recently about antivirus software for mobile devices, most notably Sprint partnering with McAfee to bring security to Android devices. I don't have any antivirus software on my Android phone. (I've had it now for about eight months.) So far, haven't had any issues. Have mobile devices been targeted to the point that this has become a pressing issue, or is this just an opportunity for antivirus companies to make some extra profit?


Dear Ben,
Malware and viruses are increasingly becoming a threat for smartphones. And unfortunately for you Android is targeted more than any other smartphone platform. Security software provider McAfee said recently that malware targeting Android phones has jumped 76 percent in the last quarter.

Of course, as you point out, this information is coming from a company that provides security products. But the reality is that Android's open nature and its growing popularity has made it a target for hackers and others looking to wreak havoc on your mobile life. But before you panic, keep in mind that the threat is still not as bad as it is for an unprotected PC.

Still, you may want to consider some antivirus software on your Android phone just to make sure you're protected. The good news is that you don't have to spend any money to do this. CNET senior writer and security guru Elinor Mills says there are tons of free antivirus software apps available for Android devices. She is also an Android user, and she uses software from Lookout. Here's a list of other free antivirus software for smartphones from CNET