Fifteen years ago, my desktop computer could transmit Morse code over a phone line. ATD;-.-./--.--H0 Somehow, that feature is hard to find in computers today.

More seriously, Wireless Application Protocol (WAP) is the problem. MMS support requires WAP support.

Older phones (and new phones that run operating systems with some history in the mobile space) support WAP because once upon a time, WAP + Wireless Markup Language (WML) were the Big Things that were going to bring the web to small screens on underpowered mobile devices. Mobiles had to support it. It was unlocking the web. It was the future!

Then web developers, by and large, skipped making their sites available in WML because doing so was a pain. Meanwhile, the screens and processors on mobile devices both continued to improve, and bringing real web browsers that could use the real web to mobile devices became the new Big Thing.

Mobile operating systems that lived through the time when WAP was king kept it around afterward, of course. However, iPhone OS and Maemo came later.

In both cases, the development teams had to decide which features were important enough to warrant the investment of limited resources--time, money, and talent--during that hectic rush to meet deadlines. In both cases, legacy technologies such as WAP, now with limited use, didn't make the cut.

Thankfully, the Maemo community is already working out what will be necessary to add WAP and MMS support to Maemo 5 though, so barring any towering, unforeseen barriers, you shouldn't be without MMS on your N900 for long.