I've not used MMS much, but occasionally have because it's the only way people with basic phones, or basic contracts (no cheap data for emails), can send and receive pictures and videos.

It's not 'must have' for me on the N900, but it'll be slightly annoying if someone sends me a picture and I can't view it, or if I want to quickly send a picture or video to someone else.

Even my girlfriend, who has a Nokia E63 which is more than capable of emails and web browsing, would not be able to receive an email from me or look at a picture on Flickr when out and about, or send me a picture she just took, because she doesn't have a phone-linked email account, finds the phone's browser too difficult to use, and wouldn't have a clue how to upload a fresh photo (come to think of it, neither would I!). But we've send and received MMS photos and videos easily.

I suspect it comes down mainly to user interface. Right now, MMS is really easy to use and understand. It's just like a text. Bluetooth is similar when you can use it

All the other options: email, Flickr uploads, sending some va text with a HTTP link, even IMs, they are *much* harder to use on most phones, and sometimes expensive too. Emails work on many phones now, but you often have to pay for "push" service, and you still have to set up an email account, work out how to use it in the phone etc. and handling pictures in emails may still not be as straightforward as MMS user interfaces. And it's amazing how many people don't have email accounts at all, even with their regular computer.

The N900 presumably makes great improvements to the user interface for other ways to send and receive pictures etc. But that doesn't help the person at the other end.