True, but you can use your firewall for SIP'n'RTP or IAX2. Creative use of firewall rules can be really powerful. For a very simple example: block VoIP from A

True, but you can use your firewall for SIP'n'RTP or IAX2. Creative use of firewall rules can be really powerful. For a very simple example: block VoIP from AWS's address ranges (serious gain). A classic response for anon calls in telephony is to make the caller record a short identifying message and then play that to the potential recipient. The potential recipient then decides whether or not to accept the call - your staff (family, whatever) become the firewall. Remember that calls are billed to the caller by the terminating provider so this is OK (caller pays). Those are two simple examples of using IP and humans to firewall telephony. Just because telephony is a bit crap on the identification side does not mean that you can't deploy lots of other weaponry to keep yourself safe. If you look deeply into SIP and IAX2, you get loads more options as well.