The introduction of EDGE in GSM phase 2+ enhances existing GPRS/GSM infrastructure, allowing 3G speeds up to 384 kbps. Unlike UMTS that uses licensed WCDMA (Wideband Code Division Multiple Access) frequency bands, EDGE is able to use existing GSM/GPRS frequency bands (800, 900, 1800 and 1900 MHz) to offer comparable speeds and compliance with IMT-2000.
GPRS and EDGE share the same symbol throughput rate but the latter uses symbols representing 3 bits instead of 1. In order to achieve this EDGE uses a new modulation technique called 8-phase shift keying (8PSK) and 9 different coding schemes (compare to GPRS which has 4).
This means consumers can connect to the Internet and send and receive data, including digital images, web pages and photographs, three times faster than possible with an ordinary GSM/GPRS network connection.
For more info visit: http://www.gsmworld.com/technology/edge