Thomasjtsi said:A CDMA iPhone 4 doesn't have a SIM slot... so that option isn't possible. Unlocking and/or flashing a CDMA iPhone can get quite pricey but... can be done.
willerz2 said:CDMA unlocks are really expensive and not worth it. As Justin said, there isn't a SIM slot for the 4, so you're limited to a handful of carriers worldwide.