I have a n800, and I use Ekiga under the account rtcomm .
It's fine, I have a softphone on a PC, so I can do video calls from a N800 to a PC.
But yeah, gets choppy with bab networks, like no less than 1.5 mb/s.
So probably it's posible .

BUT I prefer a port of AMSN (linux live messenger with video)
in the n800/810 the port its very sluggiishh!!
Maybe the N900 could have enough power ??