10-22-2012 12:36:35 AM
Try the opening a webpage in Safari with WiFi turned off. Do web pages open using cellular data? If you don't have a good cellular data connection, MMS messages won't work.
Also check your settings to make sure MMS is enabled.
General > Messages > MMS Messaging | ON
10-22-2012 08:58:06 AM
As Planet-Ed pointed out MMS has to be enabled and some have found that when doing an iOS update or restore a lot of function default to disable.