Hi, I've coded a SIP plugin for Nagios. There is some other similar plugin but it's less customizable and less powerful.
Homepage:
http://dev.sipdoc.net/projects/sip-stuff/wiki/NagiosSIPplugin
Features:
- SIP UDP and TCP transport protocols. - Customizable parameters (From URI, Request URI, server address, local UDP port, timeout internal). - The replied status code can be matched against an expected value to be considered as valid.
Regards.