Welcome to BB Forums. RIM maintains a "comparison" web site where you can check out the two side by side -
https://www.blackberry.com/Downloads...05D7C424EBAE5F
The 8700 is EDGE (works well in North America); the 8707g is a 3G device - faster data network, but does not work as well in North America (where the 3G network is on a different frequency). Actually, it barely exists.