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In [[computing]], a '''softphone''' is a [[Computer software|software]] program 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 [[Headphones|headset]] connected to the [[sound card]] of the PC, or with a [[USB phone]].

== Softphone Applications ==
A typical application of a softphone is to make calls via an [[Internet telephony service provider]] to other softphones or to [[telephones]].  Service providers may offer PC-to-PC calls for free; PC-to-phone and phone-to-PC calls are usually not free.

Another type of softphone connects to a [[private branch exchange]] (PBX) through a [[local area network]] (LAN) and is used to control and dial through an existing hardware phone. This is often used in a [[Call centre|call center]] environment to make calls from a central customer directory, and to show information on the screen about which customer is calling, instantly providing the operator with details of the relationship between the caller and the company using the call center. Some countries do not allow this PBX.

It's important to differentiate softphones from services based on softphones. [[Skype]], [[Google Talk]], and [[Vonage]] are [[Internet telephony service provider]]s having their own softphones that you install on your computer.  Unfortunately these three major providers are not interoperable, and you can't place a direct call between them.

== Communication Protocols ==
To communicate, both end-points must have the same communication protocol and at least one common audio [[codec]].  Most service providers use a communication protocol called [[Session Initiation Protocol|SIP]] (Session Initiation Protocol) by [[Internet Engineering Task Force|IETF]], except [[Skype]] which is a proprietary system and [[Google Talk]] which is based on [[Extensible Messaging and Presence Protocol|XMPP]]. Some softphones also support the [[Inter-Asterisk_eXchange]] protocol (IAX). Examples of SIP softphones can be found in the [[:Category:VoIP_software|VoIP software category]] and at [[Comparison of VoIP software]].

== Softphone Features ==
A typical softphone has all standard telephony features (DND, Mute, [[Dual-tone multi-frequency|DTMF]], Flash, Hold, Transfer etc) and a lot of new ones like Presence, Video, Wideband Audio and more.
The minimum codecs set is G.711, GSM and iLBC. Softphone vendors may offer more codecs and different feature set.

== Softphone Requirements ==
To make voice calls over Internet, you should have 

* Any modern PC with a microphone and a speaker, or with a headset, or with USBphone.
* Reliable Internet connectivity like [[Digital subscriber line|DSL]], [[WiFi]], cable or [[Local area network|LAN]]. 28.8 dial-up modem may be enough if you use a codec compressing the speech to this bandwidth.
* Account with an [[Internet telephony service provider]] or [[IP PBX]].

==See also==
*[[IP Phone]]
*[[Auto dialer]]
*[[Voice over IP|VoIP]]
*[[Mobile VoIP]]
*[[Comparison of VoIP software]]
*[[Videophone]]
*[[Computer Telephony Integration]]
*[[List of SIP software]]