Skype suffers from being proprietary and not able to be used to talk to other VOIP services.
My router supports sip VOIP and is administered via a web browser (Firefox on RO is fine). I can talk to users of sip services other than my own (eg gizmo project). Any VOIP service need to have the option of cheap dedicated hardware, to be a serious alternative to the normal telephone network, otherwise your computer need to be on all the time.
Gaim is supposed to be gaining sip support, so maybe that could be ported.