Many iPhone-ers out there prefer T-Mobile's network over AT&T's. By unlocking their phones, they have been able to use it on the magenta underdog without a problem (EDGE only, of course). If you're one of those daredevils who has parted ways with AT&T and is looking to take your iPhone over to T-Mobile, you may want to think twice before upgrading to the latest iPhone OS.
Phone Arena is reporting that Apple's latest iPhone OS 3.1.3 update breaks the ability to do a T-Mobile unlock. They also caution against upgrading iPhones that are already successfully running on T-Mobile.
"The new OS creates issues with T-Mobile's network. For example, some 3rd party apps might fail to launch (Cupertino, we have a problem), furthermore, upgrading to the new OS would upgrade your baseband to 5.12.01 which would make it impossible to unlock the iPhone and use it on T-Mobile's network. Owners of the first-gen iPhone are not affected and can still upgrade to the new OS without affecting a T-Mobile connection."
No official statement has been made by Apple, but it doesn't seem like such a farfetched thing for them to do. We've seen Apple fight Palm's ability to sync with iTunes via software upgrades, and we've seen them continuously try and beat jailbreakers. Why should customers being able to choose their own carrier be any different?