Got an old iPhone laying around?
Want it unlocked?
Ok, simply put, it has to be off contract or paid up. If you got the phone on a 2 year deal and there are still "months" left on your contract, cool your jets, this isn't for you.
If you have the phone and paid an early termination charge, or you are past that 1 or 2 year deal that gave you the "discount" on your phone, you are good to go.
AT&T will have a lot of people jumping on this today, so you're bound to be having trouble getting through. All you need to do is ask them to unlock it, and be in "good standing".
This will let you use your AT&T iPhone on T-Mobile, or just on AT&T as a backup, or anywhere else in the world that will use the GSM system such as T-Mobile in Europe and other places.
The official statement was all over the web, but you can read more at Endgadget at this link.
Since I was given an iPhone that I basically use as a portable radio, I'll be unlocking mine in case something trashes my Android phone - that I actually like very much along with my T-Mobile account that, again, I actually like very much. I just get more choice and isn't that what the free market is all about?