Do a search for CDMA and GSM to get more info. Basically AT&T/TMobile and most of the rest of the world use GSM. Verizon/Sprint and a couple other countries use CDMA. They are totally different cellular technologies and require totally different hardware. So unfortunately that means the iPhone could not physically ever work on a CDMA network no matter how hacked it was.
Given the multi-year exclusive agreement with AT&T, that means the iPhone is exclusive to GSM for at least a 3-5 years. And that would mean the chance of them release a CDMA iPhone would be approximately 0%.