According to Adriana, any of you running your iPhones unlocked on T-Mobile should hold off on installing the newest iPhone OS update. Looks like iPhone 3.1.3 breaks TMo connectivity for iPhone 3GS and 3G models - apparently the first-gen iPhones aren't affected.
Any of you running iPhone unlocked on Magenta? If so, can you confirm or deny this? Better yet, are you hard at work on a solution?
More over at Today's iPhone.