I need help, att 3650

I need to know how to unblock my 3650 with att so it can take new sims from different circuits.
Also, they charge me 30cents per kb of data that i send to or from my phone even if i'm using the ir. Any idea how i can send and recieve data without paying them cause i will never be able to unlock the full potential of the phone if i have to pay to transfer stuff. Please i'm new at this stuff but really need help. If you tell me how to unblock the phone i have a friend with a card reader and a cable and ir port who will be able to do the actual unblocking for me. Or i could possibly do it myself. Please help me out.