a PC based, software telephone that runs on your multimedia PC
a PC phone (or a PDA phone)
a software package that emulates the look, feel, and function of a phone on a computer
a software program that runs on your PC and uses a USB headset as the telephone instrument
IP telephony software that lets users send and receive calls from nondedicated hardware such as a PC or Pocket PC device. It is typically used with a headset and microphone.
A Soft Phone is a program on your computer that allows you to use your computer as a phone. You need to have a headset and microphone to use a computer Soft Phone. See also VoIP.
In computing, a softphone is a piece of software for making telephone calls over the Internet using a general purpose computer, rather than using dedicated hardware. Often a softphone is designed to behave like a traditional telephone, sometimes appearing as an image of a phone, with a display panel and buttons with which the user can interact. A softphone is usually used with a headset connected to the sound card of the PC, with a USB phone or with a "Plain Old Telephone" connected to the PC using an adapter (some types of sound cards or chatcord).
A SoftPhone is a computer program that enables a PC to become a SIP based telephone.