ohrwurm is a small and simple RTP fuzzer, it has been tested it on a small number of SIP phones, none of them withstood the fuzzing.

Features:

reads SIP messages to get information of the RTP port numbers
reading SIP can be omitted by providing the RTP port numbers, so that any RTP traffic can be fuzzed
RTCP traffic [...]

VoIP Hopper is a GPLv3 licensed security tool, written in C, that rapidly runs a VLAN Hop into the Voice VLAN on specific Ethernet switches. VoIP Hopper does this by mimicking the behavior of an IP Phone, in both Cisco and Avaya IP Phone environments.
In Cisco IP Phone networks, it first dissects either [...]

The VoIP Security Alliance (VOIPSA) is pleased to announce the public release of its VoIP security tool list. Check it out at:
http://www.voipsa.org/Resources/tools.php
This VoIP Security Tool List provides categories, descriptions and links to current free and commercial VoIP security tools.

This list was developed to address the current void of VoIP security testing resources and sites, [...]

SIP Proxy is an Open Source VoIP security test tool which has been developed by the students Philipp Haupt and Matthias Halimann during their diploma thesis and second student research project at the University of Applied Sciences Rapperswil.
With SIP Proxy you will have the opportunity to eavesdrop and manipulate SIP traffic. Furthermore, predefined security test [...]