In Europe all phones are GSM technology. In the US AT&T uses GSM and Verizon uses CDMA technology. There is no SIM card to be moved between phones as is the case for GSM. To change CDMA technology phones you must deal directly with the carrier. Regardless of what TV adds and marketeers say Verizon has for years had the best cell coverage in the US. To be honest I never tried to find an unlocked phone for use on Verizon's network. In the US, carriers subsidize the cost of phones and when you renew a contract they also give you an additional discount. For years I've gotten a new Verizon phone for free every two years.