try a battery pull first. if you already tried that, try re-sending service books. tmobile.blackberry.com (or wutever your BIS site for tmo is) and re-send service books.
I recently had my MMS not working, but fixed it with a battery pull.
Im super scared though, cause last time I downloaded the os 4.5 for my 8310 i could not reply to email, so i tried EVERYTHING and ended up downgrading to os 4.2..but today im going to be brave and try for the 4.5 again...
the download got all screwy last time and froze and gave me an error..so eh
i did the battery pull yesterday and i could send pics just fine but later that night it stopped again but this time i cant send pics to email or phones