Okay, This isn't one of those threads where I'm asking on how to do it- I'm explaining- 1) Receive your 3GS 2)Take your SIM card out of the 3G and put it in the 3GS 3)Take the other person's SIM card out of their current phone, and put it in the 3G 4)Activate your 3GS through iTunes- Pick your text message plan, and so on. 5) Activate their 3G through iTunes- Pick their text message plan, and so on. 6) Live Happily Ever After Also, if you have the EDGE iPhone, and/or don't have a 3G SIM card, just activate the 3GS with the SIM card it came with, and throw away your old SIM card. If the secondary person has an old non-3G SIM card, walk into an AT&T store, and tell them that you would like a new SIM card, they should give you one for free. No calling AT&T necessary,they will just walk you through these steps.