digi's EDGE is automatically activated already. all you have to do is just enter the EDGE settings (APN, Username and Password) for it. at least this is the case for postpaid. not sure if it's the same for prepaid.

for digi's EDGE, you've got two choices. one is pay as you use, meaning you only get charged based on how much you use. if i remember correctly, it's 10cents for every 10kb transferred.
the second choice is to subscribe to their unlimited plan which is rm66 a month and you can use as much as you want.