I have an unlocked iphone 4s and a plan with 100mb of data. I am able to send MMS messages, but the data will not work for any of my apps. I have already tried resetting the network settings, any other suggestions?
Could you go to Settings-> General, and check whether there is an option called "Profile", if there is one, remove any profiles and then try reboot your phone.
Let us know if this helps.