The S300 is the choice of large scale telephony operations. Offered as a 300 extension / 60 concurrent call PBX, it can be up-scaled to up to up to 500 extensions / 120 concurrent calls. Additionally options available include up to 3 Primary Rate ISDN trunks and up to a combination of up to 24 analogue extensions, FxO ports, 24 BRI ports and 6 3G trunks with the addition of expansion modules.