Go to “settings”
> “general”
> “network”
> “cellular data network”
> then under the “Cellular Data” the APN setting is epc.tmobile.com OR internet2.voicestream.com OR wap.voicestream.com Try each one until one of them works. No need to restart the phone.
> Turn OFF 3G because tmobile has a different frequency which will not work and will save you battery life. Turn ON roaming.
ENJOY!
**note that “t-mobile web” $10 plan works just fine!
Video also available