Starting Wednesday, when Apple is expected to reveal a new iPhone model, T-Mobile will start advertising that AT&T iPhone owners who are out of contract can switch to T-Mobile.
This has been possible for years, but iPhones on T-Mobile's network suffer a big penalty in terms of data speeds.
Now, T-Mobile is reshuffling the frequencies on its network, which will let it match or even exceed AT&T's data speeds on iPhones. For now, that will only be evident in a few spots, scattered around in cities like New York, Seattle and Las Vegas.
Verizon and Sprint iPhones don't work on T-Mobile's network.