Skype has been awesome, but I am using it on a laptop so it wouldn't be adequate for all your phone calls used this way. I use it a lot more for dial out and I tell people jokingly about my cordless phone as I walk around the house carrying a laptop to get a cup of tea or something.
I see some interesting gadgets here, but haven't investigated further. It's pretty much doing what I want already.
VoSKY - Products Center