The Fix is easy.. all you have to do is set the T-Mobile MMS Settings:
I have listed Three Methods, I know one will work for you.
Method 1
Step: 1
Go to Settings.
Step: 2
Go to General.
Step: 3
Go to Network.
Step 4:
Go to Cellular Data Network
Step: 5
For both APN fields, Type "epc.tmobile.com"
MMSC
http://mms.msg.eng.t-mobile.com/mms/wapenc
MMS Proxy:
216.155.165.50:8080
MMS MAX Message Size:
1048576
MMS UA Prof URL:
http://www.apple.com/mms/uaprof.rdf
Step:7
Press Home Key, and Restart iPhone.
Do Not press Reset Settings.....
NOTE, after restarting your phone, first send your self a text message, and then send your self a picture message.