Is picture messaging included in my unlimited text messaging for AT&T?

I pay $20 bucks a month for unlimited text messaging and I've discovered that I haven't been able to receive pictures friends have sent me nor am I able to send any pictures out. Does this mean that my unlimited text plan doesn't include picture messaging? I've read on the AT&T site that I should be able to send/receive pictures, videos, and IMs. I have a nokia xpressmusic phone and it's capable of sending out pictures, but it would just stay in my outbox. Anyone have a clue?