If not, are you certain your carrier has the same internet settings (APN, etc.)? Quite often these have to be entered manually when you switch phones to another carrier.
That said, if you guys are on the same carrier, look here:
Start on pp113-114. You may need to quickly look up your carrier's APN info, etc.
Can anyone help...?....I have been given a GT15801 and I have put my sim in and all is well ........except internet works only on wifi.
My friend the previous owner cannot remember how to toggle the 2g or 3g back on.......really frustrating....any advice please?