The Yeastar P570 IP PBX System is designed to enable businesses enjoy uninterrupted communications using its standard features. It boasts of a usage capacity of 300 users which can be extended to a maximum of 500 users using an optional D30 Expansion Module. from 60 to 120 calls . It is equipped with 16 FXS Ports, 16 FXO Ports, 16 BRI Ports, 2 E1/T1/J1 Ports and up to 6 GSM/3G/4G LTE ports.