T-Mobile USA has confirmed, via a Twitter post, that people currently using the iPhone on its network will be able to retain any legacy data plans when it upgrades its cellular network. While T-Mobile isn't an official iPhone carrier in the US, and its 3G/4G network isn't (yet) compatible with the device, people with unlocked iPhones have sometimes chosen to cope with using 2G data to take advantage of other advantages the carrier might have. In some cases, this may included unlimited data as cheap as $5 per month.
