SDK For Developing VoIP Application

Hello,
Still I am looking for a SDK that I can develop VoIP application in .NET Framework which has capability connection to ordinary PSTN phone line.
I have tried some other as well:

>>>> SIP .NET by independentsoft.com : The evaluation compiles and run but since it is SIP based, you cannot call an ordinary phone line. I have sent them an email and waiting for their reply. This is their explanation about SIP .NET:
SIP .NET is Session Initiation Protocol API for .NET Framework and .NET Compact Framework. Features includes: Digest authentication, Supports TCP and UDP protocols, Supports call holds, waiting, transfer, forward, Supports methods: REGISTER, INVITE, OPTIONS, PRACK, ACK, BYE, CANCEL, MESSAGE, SUBSCRIBE, NOTIFY, UPDATE, INFO, FEFER, PUBLISH. Create SDP message, Parse SDP message, Register, Unregister, Invite to session, Cancel session, End session, Send message, Send Info, Update session, Subscribe, Refresh, Notify, Presence, Instant messaging, Logging

>>>> VaxVoIP SIP SDK from vaxvoip.com: I downloaded the trial version. It installs easily and runs without problem. I could not test it because I do not have any SIP server! I have sent them an email and still waiting for reply.

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Ali Khademi