as far as my understanding is, its a hardware upgrade to the latest nokia masts that replace the old ones that are due for upgrade.
Edge has been rolled out to increase bandwidth outside 3G areas, to provide non 3G users with more bandwidth. (although some areas have 3G as well as Edge).
My understanding is that it is a software upgrade rather than new hardware. It is also called Enhanced GPRS.
EDGE is standard in these new masts, so it is in orange's best interests to enable the function (Orange make their most profit off data)