what cell networks are gsm
If your current carrier is set up for one, and your desired carrier set up for another, then it's likely you won't be able to use your current phone on the new network. Cell phone companies operate under one of two types of networks; either CDMA or GSM. Of the four biggest US carriers, AT&T and T-Mobile run on 'GSM' networks, while Sprint and Verizon Wireless use 'CDMA'.