My situation is a bit different. I'm testing with my wife's BlackBerry Curve 8330 and my iPhone 3G. Whenever I send her a picture message from my iPhone, and she responds with a text reply, I just get something like this:
I also had a friend test sending her an MMS message from a BlackBerry and the same thing happens. She can send MMS just fine, and reply to SMS just fine, it's only when she replies to an MMS message that the recipient receives only file info (see above).