MMS config for samsung blackjack (AT&T)?

I've got a samsung blackjack (cingular branded) that was working fine with MMS for the past few months, but suddenly tonight I can't send MMS messages. Its either an MMS outage or I have to reconfigure the phone for MMS and I'm not sure where / what I have to enter to do that. I tried googling and the results I found had different information.