So AT&T is buying T-Mobile USA for $39 billion in a deal that makes perfect sense if you are an RF engineer or a fat-cat telco tycoon, but my question is what happens to all the jailbroken and unlocked iPhones?

T-Mobile and AT&T are the USA’s only GSM wireless network operators, so if you had an iPhone and wanted to dump AT&T to allow things like free tethering, the obvious (and frankly only) way for Americans to do so was by jumping from cranky old AT&T to the much friendlier T-Mobile. And so tens of thousands — maybe hundreds of thousands — of AT&T customer did just that, and were gratefully accepted by T-Mobile.

But now with the T-Mobile brand, back office, and customer service likely to go away, will AT&T turn all those iPhones into bricks?  It depends in part on Apple, on the Apple-AT&T contract, but mainly I think it depends on terms set by regulators in return for approving the deal.

AT&T has said it will grandfather T-Mobile customers, honoring their often lower monthly fees and continued use of T-Mobile phones, but AT&T has had nothing specific to say yet about T-Mobile iPhones.

Apple hates jailbroken and unlocked iPhones, of course, and would like to see them all die, but since Verizon began selling iPhones in the USA, Apple has lost some clout with AT&T.

So my guess is that AT&T will allow jailbroken and unlocked iPhones to run on their network if the Federal Communications Commission or Federal Trade Commission or Department of Justice demand it as a condition for approving the merger, which they will if we demand it. And if that happens, the even more important question becomes whether Apple will lose some control of its ecosystem?  Will jailbreaking and unlocking — enabling iPhones to add software features and do things beyond the ken of Cupertino — become the norm?

I hope so.

Update — According to a report this morning in Forbes: “AT&T said Monday that it in the year after the closing, it plans to rearrange how T-Mobile’s cell towers work. The spectrum they use for third-generation services, or 3G, will be repurposed for 4G, which is faster.  That would leave current T-Mobile phones without 3G. They would need to be replaced with phones that use AT&T’s 3G frequencies. AT&T said it had factored the cost of replacement phones into the total cost of the acquisition.”

This would seem to suggest that AT&T will give you a free replacement for your jailbroken, unlocked iPhone on the T-Mobile network.

But wait, there’s more! If AT&T is repurposing T-Mobile 3G service to 4G, doesn’t that strongly suggest that 3G is going away completely on AT&T?  It looks that way to me. So will AT&T be giving EVERYONE a free 4G phone upgrade or just the jailbroken unlocked iPhones?

Ironic, eh?