I am running 3CX Phone System Version5.0.3790.0, using a PSTN adapter and Sipgate for outside calls. Outgoing calls on both lines work correctly, and so do incoming calls on the PSTN line. Incoming calls on Sipgate usually result in an engaged tone o the caller after some 20 seconds. They are never logged by 3CX. The few times I have got a connection the line works properly. 3CX is running on a Windows 2003 SBS system behind a 2003 SBS VPN Gateway, connected to my ISP by a SpeedTouch780 ADSL2+ Modem. If I forward ports 9000-9007 in the modem and VPN server, the firewall tests reports the following:- 1 9000 Error (4) The STUN server returned an ip which is not accessible from outside. addrFromSTUN = xx.xxx.xxx.xx:53207 2 9000 Error (6) An incompatible NAT configuration has been detected. Please check FAQ for further information. addrFromAgent = xx.xxx.xxx.xx:53215 addrFromSTUN = xx.xxx.xxx.xx:53207 3 9000 Warning (8) Local port is not blocked from outside. STUN server has returned global port different from the local one, but the local port is also accessible from outside. 4 9000 Warning (10) Port is open, but port number has been changed. In general this should not present any problems. externalAddress = xx.xxx.xxx.xx:53207 I cannot find a relevant FAQ - what am I doing wrong? If I disable forwarding in the router I get the following:- 1 9000 Error (4) The STUN server returned an ip which is not accessible from outside. addrFromSTUN = xx.xxx.xxx.xx:53340 2 9000 Warning (10) Port is open, but port number has been changed. In general this should not present any problems. externalAddress = xx.xxx.xxx.xx5:53340 Any help would be appreciated.