From Heiko Sommerfeldt
Phoner is a freeware application for Microsoft Windows, from Win98 up to Vista.
This application enables voice connections to landline, cellular network and VoIP. Phoner can be used as softphone on stationary and mobile computer devices attached to anlogue or digital (ISDN) subscriber lines and as SIP client.
YES! Phoner is freeware. Phoner can be used in privat and commercial environment, can distributed for free. Phoner is NO open source. Some more information regarding the license, see here.
SIP is the most used protocol for establishing voice calls over IP connections. By supporting SIP, Phoner can contact a wide range of peers like Asterisk and countless VoIP providers. the advantage is, that only a functional Internet connection is nessacary.
If the PC is connected to a PBX or PSTN with an ISDN terminal adapter, all supplementary services can used, that are supported by the CAPI. The PC then acts like a normal ISDN phone. CAPI drivers will be provided by the manufacturer of the ISDN hardware.
TAPI is a generic interface for all kinds of communication hardware. That can be a PBX, a telephone or a built in PC hardware. This wide range of possibilities is a disadvantage on the other side This is the reason for the stopped development of this mode in Phoner.
ISDN-Adapter with CAPI 2.0 (32 Bit); at least AMD/Pentium 100 MHz; 32 MB RAM and more; Fullduplex capable soundcard (16 Bit); Microfon and speakers