In early 2014 I installed "Update 3" (8.0.10517.150) and the "Lumia Black" software update via AT&T. After the update, everything worked fine EXCEPT MMS (the ability to send and receive pictures/videos/media through the messaging app).
When attempting to send an MMS message you receive the error:
"Can't send message Try again"
When attempting to receive an MMS message you see:
"Get media content now"
Clicking either of those links does not resolve the issue.