Yeastar S50 IP PBX Yeastar S50 VoIP 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. MyPBX S50 IP PBX supports multiple call monitor modes as well as standard features like Voice Mail, Voice Mail to Email, Call Recording, SMS to Mail, Call Detail Records, Mobile Extensions, Conference Bridge and SIP/ IAX Trunks. All these features are coming inbuilt and without any licensing charges.