Net-SIP is a toolkit for implementing SIP applications in Perl. It includes various examples and programs, like stateless proxy, nathelper, simple answering machine.
Current Version (as of 07/09/20) is 0.35, but development is active and I will not update the link all the time. So maybe you should better start from http://search.cpan.org/~sullr/ to get the latest release.
If you have questions/problems please contact the author of the module (me) directly or file a bug using perlbug. I’ll try to be responsive.