What I don't like about Group MMS on the iPhone is that all recipients' phone numbers are visible and not bcc'd like it was on the BlackBerry. Also, if you reply to the sender of a Group MMS, it automatically sends a REPLY ALL to everyone on the list. I don't realize that it is a group mms sometimes because the sender's name shows up since they are in my contacts but then afterwards I get a couple of "WHO IS THIS?" texts back from people I don't know. Annoying.
This is why I only send individual texts and iMessages.