The service works like this: you register for free over at my.gizmo5.com and then you can call any Skype user through an alias, in this form: [email protected]. It works from any SIP aware device. Furthermore, you can trigger a call by sending an SMS, which means you can call from any mobile phone, or you can even call from your web browser using a flash client.
Until now only Skype software could call other Skype users which means the many multi-million dollar Cisco Call Manager systems, the hundreds of thousands of community supported Asterisk PBX deployments, the millions of non-Skype VOIP users, are locked out of calling the largest VOIP community - Skype users.
Now, about that free part; the service is free for calls up to 5 minutes long; if you need longer calls, Gizmo5 offers a paid version of the service. For full pricing, which starts at $20 annually, check out the official site; and see how it works in an introductory video below.