When my N900 eventually fails then I will drop back to a non-smartphone mobile phone. I have several options that I like.

For pocketable open mobile device I will use something else, e.g. like the N800. Or Pandora. Or something else. There are gadgets out there which will let me run Debian or some such on a device like that.

A closed-OS smartphone is something of absolutely no interest to me, particularly the utter rubbish called WP7.