Currently there's no support for WebRTC on most mobile platforms, the notable exception at the moment is the latest version of Android running the Chrome browser.
Additionally, WebRTC does not have any native support for phone dial-in, however providers such as Twilio have begun development of WebRTC - phone interfaces (https://www.twilio.com/docs/client). Also, development of a dial-in feature would require the addition of a server to handle the authentication credentials associated with a service such as Twilio.
Video chat on the iPad/iPhone will likely be supported as soon as Apple's Safari browser adopts the WebRTC specification. However, telephone dial-in is not currently something on our immediate roadmap for the video chat widget.