Can a MM download, being sent to one phone, also go to a third party who is concurrently sending the mutual receiver a text message? I got a MM download that was being sent to someone to whom I was in the process of sending a text message; is this actually possible?  We both ended up with the MM download; the mutual receiver of both of our messages couldn't believe I ended up with the MM download that was only intended for him, and the sender of the download didn't intend for me to receive the download either.
Yes, this was possible on Android 2.2 owing to an error in Android. On versions with the bug, if you receive an SMS (or MMS) message while composing another, the message being composed has its recipient replaced with the sender of the message you received.

It was fixed in Gingerbread, as well as with an update to Froyo, but not all manufacturers or carriers may have passed the fix onto end users.