... NAT for remote IP users by DDNSRecording, Voice mail,Music on Hold,Ring group, Auto-Attendant, 3-way-conference;Embedded SoHo ... , support SIP and DDNS, Can be working under NAT; based on Linux OS, GUI for management;The RT20 is an All-in ... it also directly integrates with VoIP service provider networks. Depending on configuration when it is purchased, it supports from 8 to ...