Here is some information: http://www.ericsson.com/technology/t...les/EDGE.shtml
A technology that gives GSM the capacity to handle services for the third generation of mobile telephony. EDGE provides three times the data capacity of GPRS. Using EDGE, operators can handle three times more subscribers than GPRS; triple their data rate per subscriber, or add extra capacity to their voice communications. EDGE uses the same TDMA (Time Division Multiple Access) frame structure, logic channel and 200kHz carrier bandwidth as today's GSM networks, which allows existing cell plans to remain intact.
GPRS allows data rates of 115 kbps and,
theoretically, of up to 160 kbps on the physical layer.
EGPRS is capable of offering data rates of 384 kbps
and, theoretically, of up to 473.6 kbps. A new
modulation technique and error-tolerant transmission
methods, combined with improved link adaptation
mechanisms, make these EGPRS rates possible.
EDGE has. By adding the new modulation and coding
to GPRS and by making adjustments to the radio link
protocols, EGPRS offers significantly higher
throughput and capacity.
And here is a link to a 16 page white paper on it: http://www.ericsson.com/technology/w..._technical.pdf
As you can see they share the same base station equipment and it is also compatible with WCDMA so when people are experiencing loss of data it CAN have something to do with upgrade work being performed on the tower.