Manually configure the APN:

Go to Options -» Advanced Options -» TCP and enter an APN:

APN: wap.voicestream.com
Username: (Leave this field Blank)
Password: (Leave this field Blank)

* If that doesn't work, then please try entering the following instead:

APN: internet2.voicestream.com
Username: (Leave this field Blank)
Password: (Leave this field Blank)

* If that doesn't work, please try one more setting:

APN: epc.tmobile.com
Username: (Leave this field Blank)
Password: (Leave this field Blank)