No real detail or grit is given on the product although I would hope that it would be a SIP or at least standards-based system unlike Skype which is uses a proprietary method.

The service is said to be designed to ultimately be available for mobile devices with 3G or 4G connections so presumably the model would be direct connection or client/server connection rather than Skype’s P2P routing model.

Some more detail over in Om Malik’s article.