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What is left to gain? Some really poor applications that didn't make the cut? Use of tethering when you didn't sign up for it with AT&T? Use of T-Mobile's network that explicitly breaks the AT&T exclusivity that's legally in place between them and Apple? What is there to gain from this?
This statement leads me to believe that you clearly have not jailbroken a phone and used Cydia apps such as Lockinfo, iFile, Attachment Saver, Safari Download Manager, SBSettings, SSH, etc. There are plenty of great apps that add functionality to the iPhone that really should be there from the jump.