Microsoft Lync Server allows customers to connect Voice over IP (VoIP) calls to the public switched telephone network (PSTN) using PSTN Gateways.

Offered by third-party telephony infrastructure vendors, PSTN Gateways enable customers to extend VoIP calls in Lync to a variety of telephony configurations, including circuits to on-premise IP-Private Branch Exchange (PBX) systems and digital and analog trunks from telephony service providers.