There are a number of SIP gateways that you can use for free. You'd have to read their individual TOS and/or trust them about tracking and monetization. One of

There are a number of SIP gateways that you can use for free. You'd have to read their individual TOS and/or trust them about tracking and monetization. One of the other guys that's working on this has a list of a few providers that offer a free account and work with the WiPhone. I'll see if I can post it once he's here.