Cell phones: MMS messaging problems with unlocked phones on Cingular

MMS messaging problems with unlocked phones on Cingular

I am a Cingular customer and I recently purchased an unlocked Sony Ericsson k790a. I love the phone except for the fact that when it comes to MMS messaging. I can send pics and videos that have pretty beefy sizes. However when people send pics or vids its totally different solution. Any pic gets squashed to a smaller than thumbnail size and videos simply will not play. I recieve a "One or more of the message components have been deleted by mms adaptation" message instead. Is there ANY possible way to have full mms capabilities on a unlocked phone through cingular?

I am in dire need of some kind of solution here.