An open source softphone is similar to a landline or mobile phone, but with one major difference: The phone call is conducted over the Internet. To work with other phones, an open source softphone must be able to integrate with phone networks and support a large range of different protocols. When someone makes a call with a softphone, he or she either uses a universal serial bus (USB) headset or a microphone embedded in the computer; the softphone must be able to integrate with the device for effective communication. Depending on the user's desire for privacy, a secure softphone will keep people from hacking into the line and listening to conversations. Standard call features also will help separate the good from the best softphones, whether open source or closed.
Aside from being free or low-cost, open source softphones have other advantages over closed source versions. The source code for the program is open to the user, allowing developers to alter the coding and sell the modified version. If the user does not know programming languages, then he or she can usually download modules made by developers to add new functions to the softphone.
When someone uses a closed source or open source softphone, it uses certain protocols to transmit the user’s voice over the Internet to another phone. For this to be successful, the softphone must be able to understand and work with many different protocols. If the softphone only understands a few protocols, then phones under some phone service providers will not be able to hear the softphone user. The more protocols supported, the more versatile the softphone.
To talk into the softphone, and to hear the other person talking, there are two main options for users: a USB headset or the computer's microphone. While a USB headset is usually better, because it is more convenient and provides better sound quality, some users may not have a headset. Due to this, the open source softphone must be able to support the preferred communication technique of the user, or support both, so the user can switch back and forth as desired.
As with any service that works over the Internet, security is an issue. An unsecured open source softphone will be easy for hackers to get into; this means they will be able to listen to the conversation and may be able to inject viruses into the phone line, targeting both the computer and the phone. This means the best softphone must have at least standard security features, such as encryption and authentication systems.
An open source softphone is like a regular phone, so it should come with standard call features that make a regular phone useful. Some features include call holding, a history of calls, call transfer, conference calls and call recording. A user should pick a softphone that has features that support his or her calling needs.