I think a much easier way would be to use Pidgin and try to fix what's lacking there (either by supplying patches or by reporting bugs and being a bit active in the forums/mailing lists) as it's way more probable that you would get the functionality you need in the N900 Pidgin than hoping some company would release a N900 version of Ebuddy.

Personally I'm very happy with the built-in IM which I use most of the time, but I also like remote irssi/bitlbee over ssh from home which I normally use.