The title says it all... I will soon be getting my old iPhone4 unlocked through the new AT&T policy. Part of the procedure requires me to backup/restore with iTunes. Will updating the OS (and baseband) to the latest version work if I plan to use my newly unlocked phone with T-Mobile? Jailbreaking is not important to me right now, at least not at the moment. I just want to make sure T-Mobile will work on newer basebands, as it is nearly impossible to downgrade basebands if I make a mistake by upgrading to a newer one. Thanks!