Yeastar S50 50 Users 25 Concurrent Calls Modular IP PBX Yeastar S50 IP PBX is a compact and full-featured IP-PBX that comes in a 19’’ 1U rack-mountable chassis. The advanced module-based S50 is capable of supporting ISDN BRI, PSTN, and GSM connectivity, providing VoIP communications for up to 50 users....