Those phones are for people who travel, the rest of the world uses GSM like AT&T and Tmobile. This way people can put in a SIM card from over seas and not have to switch phones to use the GSM networks around the world.
It is NOT possible for the iPhone to work on Verizon's network, it just isn't and never will (until there is a CDMA version or in the future when Verizon and AT&T both have their 4G LTE networks up and running). The iPhone does not contain a CDMA radio, Verizon's network does not work with GSM phones. Verizon phones that have SIM slots work on CDMA in the USA and GSM every where else.