Maybe I'm way off base here...
The reason one would send an mms through email is because their phone has no true MMS functionality. So they would send out MMS's (through email) to other people's phones who do have MMS functionality. In turn those people could MMS to the iphone by sending it to their regular email address.
Since the iPhone doesn't support MMS, what exactly do you expect to happen when you send it to an MMS speciffic address? Where do you expect it to show up in your iPhone? Your email box? because that's just a regular email box that is in no way connected to your phone number.