A few shops local to me do iphone unlocking so they can be used on other networks.
Ask them what firmware revision these phones have and find out if it is SOFTWARE unlocking, or if they are using a SIM hijacker. SIM hijackers are little bits of circuitry that fool the iphone into thinking it has a valid network sim in it. Problem is, they don't always work, many don't allow a 3G data connection, and they are VERY tempramental. Google REBELSIM or TURBOSIM