Have a jail broken iphone and you want to connect it to tmobile data plan? Follow this tutorial and learn how. I am using a Jail broken iPhone 3.0 with the $24.00 smart phone plan from tmobile. People used the 5.99 plan and it worked also. With this plan i was able to connect to my mail, view web pages and connect to youtube.
This process worked for me.
Click on settings
Click General
Click Network
Select Cellular data network
Now select APN and type in epc.tmobile.com restart the phone and it should work with no problem.