GSM/UMTS

           Only in America are CDMA devices very popular which says a lot as CDMA is constantly ageing. GSM devices have ruled over seas and in domestic areas the best thing about GSM is you can put in a SIM card and continue using your service. However doing that can cause certain features such as HSPA or LTE to not work and as a result the device can be useful or useless.

          GSM based devices use HSPA,UMTS,EDGE,GPRS or LTE the huge advantage that GSM has over CDMA is the universal ability to change service providers however some carriers may choose to "lock" their devices to keep it on their network however you can "unlock" by entering an unlock code. Airwaves provide the way for wireless devices to communicate and different frequencies like 850MHZ can talk to 1900MHZ. With that being said you will want to check your device's frequencies and the carrier you want to switch to frequencies as having all frequencies but one can result in having only EDGE. That is the thing that people don't seem to give Apple credit for as the iPad and iPhone have LTE and GSM and CDMA radios and don't disappoint on performance unless it is a bad radio or network if you have Sprint. I personally recommend a world phone that can be unlocked for another network like O2 so if you come to the U.K for example your AT&T phone will use O2 and vise versa. Another thing people don't seem to credit Apple for making a dual CDMA and GSM radio so if you have Verizon or Sprint or any other CDMA carrier you can use a GSM carrier for back up or just left Sprint.