i will be quite direct: don't buy an new n900 now.
it does not worth. not ewen in 2011 does not worth buiing.
buy a newer phone, with better support.
as much as i praise the work of the guis aound here, i can't lie to u.
u can feel the lack of nokia support, the software is preety old, and we are fighting to keep it on date.
i don't know what are your exact needs, but i think u would like a phone with more than a month active support.
for me, recaller did not worked wery well, some random recordings, some all time recordings, etc

in any case, good luck with your research