EDGE or Enhanced Data rates for the GSM Evolution is a technological evolution of the GSM and IS-136. Goal of developing this new technology is to increase the speed of data transmission, spectral efficiency, and allows the use of new applications and increase capacity.
The application of EDGE in GSM phase 2 + such as GPRS and HSCSD done by adding a new physical layer at the side of the Radio Access Network (RAN). So no berubahan on the side of the core network such as MSC, SGSN, or GGSN
Source : http://id.wikipedia.org/wiki/Enhanced_Data_Rates_for_GSM_Evolution