Settings-> General-> Network-> EDGE->
Add this to the APN field:
internet2.voicestream.com
Leave the other lines blank. Back out of settings and try a page in Safari. The dreaded "not subscribed to edge" message should be gone. Firmware 1.1.1 and below will not save the APN setting on a hard reset.

I have t-mobile 5.99 plan for the internet for the Iphone. I have done the steps it takes to get it to work. It is working, however it is extremely slow. Most of the time it wont even work. Is the connection on this plan suppose to be that slow? Please help me with this situation. Thank You!