In this article, we are going to talk about the open source telephone system called FreeSwitch. This system can be used as PBX station. It should be mentioned that FreeSwitch works on Windows, Mac OS X, BSD, Solaris and Linux. FreeSwitch developers participate in other open source projects and contribute to Asterisk, SIPX, CallWeaver. FreeSwitch supports various protocols, such as SIP, H.323, IAX2, which allows you to interact with sipX, OpenPBX, Bayonne, Yate, or Asterisk.