It doesn't show up as a multimedia file. If the person you are chatting with doesn't have iMessage, it sends as a regular sms or mms.
I think the mm in MMS stands for multimedia. This has to be downloaded and is indeed a picture of an SMS message. It is white text on a black background. I ONLY get this when the iPhone is sending to multiple senders. Otherwise, I get a plain text message. The bad part is when the group is big, it is hard to keep up with the messages as it take the phone a while to download the MMS messages.
I knew /. had certain technologies that can't be criticized but it is strange to see the truth modded to flamebait.