cellular data network and put these setting and reboot your iphone
Cellular Data
Apn: wap.voicestream.com
Username:
Password:
Mms
Apn: epc.tmobile.com
Username:
Password:
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