Hi.. Try This & Follow in Order:
How to Enable SwirlyMMS
-Installer > Sources > Add this repo:
http://swirlyspace.com/SwirlySpace.xml > Install VERSION 0.3.6
-Install > Swirlyspace > SwirlyMMS > Install
-RESTART iPhone
-Launch SwirlyMMS enter the following SwirlyMMS T-Mobile (USA) Settings:
MMSC: 216.155.174.84/servlets/mms
Proxy: 216.155.165.50:8080
MMS-APN: wap.voicestream.com
User: empty
Pass: empty
How to view MMS:
Preview > Open > Apple Icon > Up > Up > Double Click Media > Double Click Mmsfiles
To view the pics (full size) select modify - open with the preview.app
To view the text sent with the pic select modify - open with textedit.app
P.S. Receiving mms works with wifi on too!
If you're receiving MMS messages but the attached photos are very small (160x120 in my case) you can attempt to correct this by adding the following source to installer:
http://swirlyspace.com/SwirlyMMSSettings/Settings.xml
You will find a new category called SwirlyMMS Phone Faking which will allow SwirlyMMS to pretend to be another handset that may be supported by your carrier.
In my case, I use T-Mobile USA and the Sony Ericsson w800i profile works beautifully for me...
Enjoy