If you're going the (local or remote) supl-proxy route, which I intended to try as soon as I can get a Maemo dev environment set up, I strongly suggest you have a look at the open databases of cell IDs and wireless APs at http://openbmap.org/ and http://www.opencellid.org/ - I think prehaps with ephemeris data added, these could make a much better, more accurate, and open, SUPL server than we can currently get.

I think the Maemo app CellNet-info uses one of those sites to provide lat/long info for a cell, but I'm not entirely sure at the moment.

An open SUPL server would benefit not only the N900, but virtually any modern phone.