SIP trunks are VoIP trunks from service providers, enabling enterprises to create a single, pure IP connection to carrier clouds. Voice is layered on top of the network with other IP applications, traversing routers, switches, firewalls, and users with non-SIP phones can make and receive SIP calls. This rfa enables 20 SIP trunks. License key is available for the IP Office Small Office Edition, 406v2, 412 systems running Release 4.0 software, and IP Office 500 Standard or Professional Edition