I have executed a search for any related MMS issues related to the one I am having, but did not seem to find anything; If I overlooked it it, please accept my apologies.
The issue that I have experienced is that I will send an MMS message (picture message to be specific) and my phone will show the time stamp of when it was "sent." However, I have noticed that many times, it will not actually send until the other person has sent me a picture message in return, or it will just be delayed several days.
I sent someone a picture on Monday afternoon. They just received it on Wednesday morning. On Wednesday morning, I was attempting to send someone else pictures. Person 2 said the sent me a picture, however, I have yet to receive the picture.
After performing a reboot, nothing seemed to change.
Samsung Galaxy SIII running CM10-20120729-UNOFFICIAL-D2ATT