Is there a CDMA version of the Iphone other than the new Verizon one?
Sprint is CDMA (not GSM and SIM card) so I highly doubt you can, unless you have a China/Japan Iphone that has CDMA and GSM capability.
I have a Touch Pro 2 on Sprint ( Iphone 4 is comming) and it has both network capabilities, Sprint refers to such devices as 'World phone' because once out of NA/CD almost no one uses CDMA so you would switch to GSM and find the network Sprint buddies up with in that country.