It's not entirely predicatble, but I'd say my e75 lasts longer idling on IRC by itself than serving out internet to N810 idling on IRC. Certainly on my old Nokia 6820, serving out internet over bluetooth uses huge amounts more..

hopefully IPv6 will arrive soon, and hopefully ISPs and operators wont **** it up into a similar mess as with IPv4. That would give lots of power savings for the mostly-idle use cases of IM and push email.