The iPhone 5 will be a dual-baseband device that operates on both GSM and CDMA networks. According to comments made by Verizon CFO Fran Shammo in the company's last quarterly earnings call, Apple's next iPhone will be a "global device" compatible with all carriers.
Shammo was the one that leaked the information that Verizon would be getting the iPad 2, so there's reason to believe his claim is true.