VoIP Application in .NET

Hello,
I am desperatly looking for a SDK which I can develop a VoIP application that can make call from PC to (PSTN) phone line. This SDK should be able to connect SIP protocol to ordinary phone line.
If you search on the web, you will find a lot of people who claim have the best SDK but according to my experience, they do not do what I am looking for.
Here are some samples:

>>>> Conaito VoIP EVO Enterprise SDK: do not support PSTN. It is only a voice messenger and it is channel oriented which means you cannot wake up other party. Other party should be on-line already!
Here is Conaito's explanation: The Conaito VoIP SDK contains a hight performance VoIP conferencing client capable of delivering crystal clear sound even for both low and high-bandwidth users. The enlarged version of the Conaito VoIP EVO SDK enables to record calls and this can be very use full for recalling discussions with....

>>>> SIP VoIP SoftPhone by abtollc.com: Their trial version does not work and they even did not bother to reply to my emails.
Here is their explanation: Our brand-new VoIP SIP SDK provides a powerfull and highly customizable solution to quickly add SIP based dial and receive phone calls features in your software applications. It accelerates the development of SIP compliant soft phone with a fully-customizable user interface and brand anme. The Abto LLC VoIP SIP SDK contains a high performance VoIP conferencing client capable fo delivering crystal clear sound even for both low and high-bandwidth users and SIP compatible devices. It supports STMF, adaptive silence detection, adaptive jitter buffer....

>>>> VoIP H323DLL v1.1 by Research-Lab.com: It claims some capabilities but the trial version does nothing important. It tried .NET sample and even I could not compile it in the first place. After a tricky compile, sample throws exceptions at time of showing main form! I have sent them an email. Still I have not received reply....

>>>> VoIP SIP Phone DLL by Research-Lab.com: It claims allows to make PC-PC, PC-Phone or Phone-Phone calls or create Instant Messaging (IM) sessions over the internet and SDK brings protocol support for ActiveX and it eases implmentation of a customized VOIP solution eliminating PSTN lines. In practice when I downloaded this SDK and installed, I found it very similar to VoIP H323DLL v1.1 (see above) and although .NET Sample compiled, it did not work at all! Again I sent an email to vendor and I have not received a reply yet.

>>>> SIPEK SoftPhone: This is an open source but either it was too professional for me or it did not work. Still I am not sure if it supports connection to PSTN. This SDK works based on SIP and demo did not worked for me. Sample C# application also does not work as it assumes some default port/host/uid/pwd/proxy.

At the end, somebody please give me a clue about where to look for a SDK.

Be a winner in your daily challenges
Ali Khademi
علي خادمي