The CDMA model does GSM as well:
http://www.apple.com/iphone/specs.htmlCDMA model A1429: CDMA EV-DO Rev. A and Rev. B (800, 1900, 2100 MHz); UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 1, 3, 5, 13, 25)
The CDMA iPhone 4S was the same (minus LTE), it has a SIM card slot for global roaming and everything.