Edge Data is a large concern for some users (and going over). I am in Canada, hence the following idea.

Make EDGE useage visible: create a program that a user could enter their monthly max data and it would show somewhere (somewhere or) on the home screen... AND, have the ability to automatically disbale EDGE when the limit is reached, with a 5% remaining (something like that) notification. Also, a programmable reset date would be good for the months you don't exceed useage but are in a new billing cycle.