US residents can call for FREE using a Linksys PAP2 and Google Voice

See here.

The Linksys PAP2 is a little box that turns any home phone into a full-fledged VoIP phone. It’s so simple: You just plug your home phone into the PAP2’s jack and plug the PAP2 into your home network. That’s it; your hardware setup is done. The real magic (and work) lies in the VoIP service we’ll use: Sipgate, a VoIP service that gives you a free phone number.

When combined with Google Voice, it’s as perfect a solution as $0/month will buy you: Sipgate gives you free incoming calls and Google Voice gives you free outgoing calls. You won’t notice any difference when it comes to receiving calls—your home phone will ring, just like it did with your landline. Making outgoing calls is a little less convenient because you’ll need to use Google Voice’s website to set up calls but that tiny trade leaves you completely free of monthly dues.