This phone should switch its mode from landscape to portrait. so the landscape mode will be the alternative option for the users.
You're right, N900 is and must be mainly landscape. But daily use needs at many times portrait. And not a perfect portrait is needed, I mean, if desktop icons are rotated, square widgets are rotated, and not-square ones are maintained, that could be PERFECTLY USEFULL! , you must "turn your head" to read what song is playing at media widget? what a problem. And still full one-hand usefull. (I don't know if using correct verbs in this post, excuse me if wrong ones)