Программный телефон VoIP / SIP C # WPF

Мне нужно написать VoIP / SIP Soft Phone на C #, используя интерфейс WPF только с поддержкой звука. I need to have call transfer, call conference, and recording of conversations in mp3.

I've looked at VoIP SDK from ABTO LLC, but it is slow at application startup (30 seconds to start application, I think it's related to loading activex part of this sdk).

I've also looked at SIP.Net, but it's only for SIP and doesn't contain components for voice data transfer.

I have very limited time only 2 months from zero to fully working app.

What SDK can I use to accomplish this task?

Windows 7 must be supported.