If you want to complete all the features of the softphone, the main ones that I know are NCH ββExpress Talk and pjsip . I never tried to integrate with any of them, and I donβt know how easy or difficult it is to do this with C #. If you only need your application to be able to enter and / or manage calls, you can use any open-source SIP stack, C #, which is sipsorcery .
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