Feedback about an SDK

Hello,

My question is not really about C#.

I have just started my company and would like to have an own webphone in order to give better customer service. I came across an SDK, Ozeki VoIP SIP SDK (http://www.voip-sip-sdk.com/). On the website I have read that it is written in C# but here nobody has experience in that programming language. Before hiring a C# programmer I would like to have some feedback about this product.

Has anyone used this SDK previously and willing to provide me with information based on personal experiences?

I mean how stable it is, how easy to use it, a few words about support.

I really appriciate any feedback.

Thanks in advance.