Phone calls with static

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To a certain degree Wireshark could be of use here. If you can capture the network traffic related to the phone call on various locations in the VoIP network, and use the RTP player function to listen in on the call, you should be able to get an idea of the quality of the voice in the VoIP part of the voice circuit. However, this is only part of the voice circuit, according to your description. Other components, eg. the TDM fork, VoIP gateway, etc. come into play as well.