Windows Phone 8 VoIP SIP Provider

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C#

Windows-Phone-8

I want to develop an app with VoIP and sip. I have found a good example from Microsoft sample is ChatterBox VoIP sample app

From this app we can receive or make audio or video call to some one.But I can not call to another number.

In this document VoIP apps for Windows Phone 8

the incoming call is possible through Microsoft Cloud server. It will push a notification to our phone.

I have also found some third party SIP clients for Windows Phone 8 like LinPhone and PJSIP but they are not providing how to use that thing

Now my questions are :

1) How can I integrate SIP client to this ChatterBox example or How can I call to another number?

2) Can it is possible to user other that Microsoft Cloud server means can I use my own server to push call to my app?

3) In ChatterBox example there is a default incoming call. How can I call from another to my number / my app ?

Thank You.