Can't be done.
So far as I know Ajax Apps are sandboxed and so they can't access your iPhone to retrieve any photo file or any such crap, not to mention it does absolutly not have any access to the phone hardware in order to be able to send the damn thing via the cellular network.
Forget about MMS, it is a mostly nieche and useless feature anyway. Simply accept that despite the advances of the iPhone it does not have MMS. Maybe, just maybe if enough people b*** about it enough it might be added in a future firmware update, but then instead of doing it on forums do it in an e-mail to Apple.