If the access Technology and Accessability to all three Bands in GSM ( 900,1800,1900 ) one can use the GSM Phone everywhere….in the world…but still he can use them in some caribbean island where they have GSM but Freq is 800 MHZ.
CDMA Access Technology and Band differs from GSM…So the equipment need such a capability to access this technology also.
Currently there is no user end equipments for this pupose but they are in developments….
Rgds