This reminded me Richard Stallman's notes about the newly emerged Cloud Computing. He defined the CC as untrustable and advised to avoid.
I'd suggest IP Telephones. Most of them are capable of making direct P2P connections without even any VoIP server. They only need an external STUN server to arrange the NAT configuration if you use the IP Phone behind a NAT router (which is almost always the case) There are many free and realiable STUNS servers running on the Internet or you can construct your own.
SIP/SIPS is nice. You can just use your IP[:port] as your phone number, and forwarding the required ports isn't too hard either if you're behind a NAT.
I'd suggest IP Telephones. Most of them are capable of making direct P2P connections without even any VoIP server. They only need an external STUN server to arrange the NAT configuration if you use the IP Phone behind a NAT router (which is almost always the case) There are many free and realiable STUNS servers running on the Internet or you can construct your own.