Just read an article on Emerillon ( http://www.novopia.com/emerillon/ ), a project which aims to become Gnome's map viewer:
http://blog.pierlux.com/2009/10/06/a...map-viewer/en/

Looks like it uses OpenStreetsMap. It has a plugin-based architecture. One idea for a plugin mentioned in the blog post is for telepathy integration.

I'm not really a developer, so I don't know how applicable this is to the N900 - but looks like it might be worth keeping an eye on, so I thought I'd point it out to you Maemo folks .