Mutli Functional IPPBX with Optional FXS/FXO/GSM/VoLTE interface on a single gateway Upto 4 Modules/Ports, Built-in SIP server, support up to 1000 SIP extensions, Support up to 200 concurrent calls with 3 Years Warranty, Support voicemail/recording and VPN server/client (Modules to be Bought Seprately)