I cannot send nor received text with media content on my ATT unlocked Nokia Lumia 820 after the Lumia Black update. Please send me suggestions to fix this?
You need to set your APN settings manually.
Similar problem has been occurred in Lumia 920.
Try this.. It might help you.. !!
Tap access point
You may see an access point for your carrier like "AT&T" listed as "active".
This is the one that is not working with MMS.
Tap the + icon at bottom to add a new fake access point.
In the "Name" section, under "Connection name", enter any name like "fake".
In the "Internet APN" section, under "Access Point Name", enter any name like "fake apn".
The checkmark icon at the bottom should now be available for you to tap it so you can save this fake profile, tap it.
Back in the access point list, tap the fake access point you just created to switch to it. Wait until it says that it is active.
Tap the back button.
Go back into access point menu and notice that your "AT&T" (or your carrier) access point is there, but it listed as "inactive" now.
Tap on it to make it active again and wait for it to say "active".
Send an MMS picture message, your MMS should be working again.
Also check this below thread..
If The above steps didn't Fix the problem you can try out the below steps: Corrupt/buggy backedup mms text message in my saved text messaging account. I will now provide the instructions to fixing the MMS problem:
NOTE: This worked for me because for my 920 I had text message back up on and if yours is off, then it might be because of something else.