Skype is currently the VoIP solution that everybody is talking about unless you just want cheaper phone calls then you are probably using one of the mainstream suppliers that give you a plugin box and no need for a PC to be on.
Today I may have found a comprimise in wengophone they do a really nice
VoIP client that can do voice, video, sms and chat. It uses SIP and
other open protocols to make it play nice with others. But for me
the big plus is that it looks like it works with a normal web
proxy. So now I can have VoIP setup at work! I am not to sure how
well this would work with all these extra stages there may be a bit
of a delay but it must be worth a try.
If you want to give it a try call me at choffee @ wengophone. Might want to start with a IM chat first to see if it works!