After a lot of effort we have managed to successfully (and consistently) send MMS messages from Series60 phones (both with and without SMIL), using a simple HttpConnection POST to the MMS Server.
But we have not managed to replicate this success with Series 40 phones. I suspect that we fail because while the Series60 phone lets you choose the Access Point to use ( the user must select the MMS access point), this user dialog does not exist in Series40 (really, how does one set the access point for Java HttpConnections on Series 40 ???)
Anyway if you have any experience on MMS in Series 40, or if you simply know how Java uses Access Points on Series 40, please reply to this post!