I got it working!
I put my SIM in a friends phone, called AT&T's After-Hours Center (1-866-801-3600) and told them to activate my MMS.
The guy kept saying 'Are you sure you don't have an iPhone?'
I, of course, said 'Yes, I'm sure!'
He said it should work so I put my SIM back into my iPhone 3GS and went to http://text5free.net (CHANGE THE 5 TO A 4) and sent myself a test-MMS.
It works!
Anyway: Screenie:
I put my SIM in a friends phone, called AT&T's After-Hours Center (1-866-801-3600) and told them to activate my MMS.
The guy kept saying 'Are you sure you don't have an iPhone?'
I, of course, said 'Yes, I'm sure!'
He said it should work so I put my SIM back into my iPhone 3GS and went to http://text5free.net (CHANGE THE 5 TO A 4) and sent myself a test-MMS.
It works!
Anyway: Screenie: