I inherited a used 3g, which, even though old, was better than the cheap gophone I had been using. The 3g had previously been on AT&T (even though it was a contract and not prepaid). Unfortunately, a simple swap didn't work. I eventually downgraded ios to 3.1.3 and jailbroke it. However, since it seems to be impossible to change the IMEI number to match my old phone, I think I'm stuck. Is it possible to buy a new $10 go phone just for the SIM, then activate that sim for the iphone?