Sprint is a CDMA network .. it doesnt use a SIM card like GSM networks (ATT/T-mobile)
If you want to use the pre on a GSM network you need to buy a GSM palm pre.. and they are
not cheap.
If you want to use a palm pre on Sprint/Verizon you should get a sprint or verizon specific pre... I *think* people are able to use their pre on metro pcs and cricket.. but that requires some modifications