That's basically right. MMS is surprisingly complicated and difficult to implement.

- It doesn't run over SMS.
- It doesn't run over your regular data connection either.
- It needs the ability to open two simultanous data connections, if you want you N900's normal data to continue working.
- It causes a clash of IP network addresses when both data connections are active.
- It needs special settings for each operator.
- Just like regular GPRS data sometimes needs you to enter special settings on the N900 because the defaults don't always work out of the box and the operators don't have specific N900 support yet, only MMS is even less likely to work out of the box and the right settings are harder to find and even harder to test.
- When operators do support the N900, like other phones it'll be be by sending service command SMS to update the phone settings, so handling of those will be needed.
- That means service command UI too.
- There's more than one way to recieve MMSs, depending on the operator.
- You need a special MMS browser to display them, because they have features like animation, sound, video and scrolling text sequencing, not just showing a static picture.
- Someone has to figure out how to fit that into Conversations sensibly. Thumbnails?

Unfortunately almost every part seems likely to have to be rewritten for Maemo compared with Symbian, although a few bits and pieces might be usable, and much of it would make handy reference code