I spent ages trying to find ip addresses for Skype's servers for their Sip gateway service. Fortunately their technical support team were very helpful and provided the ones below. Might prove useful to those of you wanting to tighten your firewall security.

63.209.144.201

204.9.161.164

193.120.218.68

80.252.85.76

78.141.179.70

Besides the 5060 port that needs to be open the only other ports that need to be open are 8000-80xx where xx is a multiple of two per channel.

Hope this proves useful.

3CX, the makes of the popular Microsoft Windows-based IP Phone System have released a security update for their 3CX Phone System 9 installations. There are no details of what particular vulnerabilities have been addressed by this update, except that it addresses vulnerabilities when using bridges to connect to other 3CX phone systems. Details of the update and further recommendations for securing 3CX installations are available in the 3CX announcement of the release.