The following information should be set in Settings->General->Network Settings->Cellular Data

NOTE: THE FOLLOWING IS SPECIFIC FOR TMOBILE CUSTOMERS

APN: wap.voicestream.com
MMSC []://216.155.174/servlets/mms
MMS Proxy: 216.155.165.50:8080
MMS UA Prof URL: []://www.apple.com/mms/uaprof.rdf //This section is optional



TIP: REPLACE [] WITH STANDARD HYPERTEXT PROTOCOL.
TIP: REPLACE WHATEVER IS BETWEEN THE [] WITH YOUR INFORMATION.



Hope that helps!