PhonerPhoner 
Phoner (phoner.exe). TAPI is a generic interface for all kinds of communication hardware. It can be a PBX, a telephone or a built-in PC hardware.
Phoner is a versatile application designed to facilitate high-quality voice connections over landline, cellular, and VoIP networks. Whether you're using a stationary or mobile device, Phoner acts as a reliable softphone, supporting both analogue and digital subscriber lines (ISDN) as well as SIP connections. Its compatibility with a wide variety of devices ensures a smooth communication experience, whether you're making calls from your PC, laptop, or mobile device.
With SIP being the most widely used protocol for voice calls over IP, Phoner allows you to connect with numerous peers, including Asterisk servers and various VoIP service providers. All you need is a functional internet connection to get started. For advanced features, when connected to a PBX or PSTN system through an ISDN terminal adapter, Phoner supports supplementary services provided by CAPI. The result? Your PC functions just like a traditional ISDN phone, offering full compatibility with ISDN services when used with appropriate CAPI drivers from your ISDN hardware manufacturer.