An interface is provided between a conventional telephone and a conventional computer configured for network voice applications including a sound card and modem. The interface allows for use of the telephone during network voice applications such as IP telephony and voice chat. When the telephone is not used, the interface allows for sound to be input and output via the computer sound card and conventional computer microphone and speakers. When the telephone is picked up off-hook, the interface senses the off-hook state, causes the computer sound card to be connected to the telephone instead of the conventional microphone and speakers, and allows for network voice applications to be conducted using the telephone. Various alternative embodiments of the invention allow for signaling of the telephone hook state to software resident on the PC for controlling network voice applications, for sensing DTMF signals in accordance with keypad entries on the telephone to control initiation of phone calls and voice chat sessions, for generating dial tones and busy signals, or other sounds and/or voice messages, in accordance with the telephone hook state and the telephone line status, and for permitting the telephone to be controllably connected to the PSTN for making standard PSTN calls in addition to calls involving network voice applications.