S20 - is a PBX of VoIP technology. It has all the functionality that a telephone exchange can have.
IP phones: 20Simultaneous conversations: 10Number of trunks: 20Analog Ports (FXS/FXO/BRI): 4Wireless channels (GSM/3G/4G): 1
Yeastar_S_Series_VoIP_PBX_Datasheet_en.pdf