I just bought a used 3g iphone. I am currently paying $20/month for att's 2g iphone internet plan. Now, everything works, but I can't tell if my internet is still 2g or on the 3g network. Do I have to go into the att store and sign up for the $30 plan to get the 3g network or is it already on here? I put my sim card in but I can't tell... Is it supposed to say 3G in the top corner?