Is there a SIP library for Windows Phone 7 yet?

Question

Latest developments: Windows Phone 8 now officially includes support for VoIP, but it's basically just an extension of the existing Push Notification architecture, meaning the API only facilitates notifying a phone of an incoming call and allows having a familiar call screen.

There still isn't a SIP library (publicly) available, as far as I'm aware.

Original Question: I am currently in the process of designing (not implementing yet) a Windows Phone 7 application that our team thinks should use SIP (the VoIP standard). With the new Mango SDK, this should be possible, since sockets are now supported.

Here's the problem though: None of the team members (including me) have any experience whatsoever developing for .NET, and we're working in a pretty tight time frame already (less than two months for implementation, starting early next year), so developing a SIP library from scratch is not really an option.

So, here's the question: Is there a freely usable (either OSS or proprietary, like a Microsoft API) SIP library for Windows Phone 7 (Mango)?

Also, if you aren't aware of any such library, how do you judge the chances an inexperienced team such as mine could succeed in porting existing libraries such as PJSIP or ReSIProcate?

Or, finally, is there an easier route to using some sort of VoIP on Windows Phone 7? Doesn't necessarily have to be SIP, but a protocol with a readily modifiable server available is needed.

(Foot note: I'm new to Stackoverflow. It seems to make sense to me to ask these three questions together. If more experienced members disagree, I'll happily split this into three separate posts :) )

Edit: I don't know how much use this will be for other SIP / VoIP projects, but my team decided to go with the Silverlight Video / Voice conferencing Modules from Socketcoder - they implemented the G.711 codec in C# and created their own protocol to transfer it from client to server. Because we are inexperienced in both C# and network programming and have to meet a deadline, we decided to go with this and expand it for our purposes (distinct users, security features etc.) rather than try to wrap our heads around the SIP standard.

Answer 1

Look at that http://sipsorcery.codeplex.com/

This is not WP7 library, but they have Silverlight version. So it could be converted for WP7.