Hello, I have an factory unlocked AT&T iPhone 4S that i gave to my wife to use on T-Mobile. I've followed all the tutorials on the web but i still can't get MMS to work. I have successfully turned MMS on in the settings, but when I go to send a picture message, the sent status bar just hangs right before it finishes sending and fails. I read something somewhere that I need to edit the plist, how do I do that without screwing the phone up? Any advice would be greatly appreciated.