Voip

I made a small Rust VoIP.ms CNAME blocker.

The short version is that I wanted to block a caller by name instead of by phone number.

This sounds like it should be a normal checkbox somewhere. It is not.

The missing filter

VoIP.ms has a pretty capable CallerID Filtering feature. You can filter on specific caller ID numbers, phone book groups, anonymous callers, calls that do not match the North American number format, STIR/SHAKEN attestation level, and wildcard patterns like area-code-ish blocks.

That is all useful. Unfortunately, it is also very number-shaped.

There are callers where the number is not the stable part. The useful part is the caller ID.

VoIP.ms even has a blog post on stopping spam calls that frames call filtering around numbers, area codes, and anonymous caller status. In the same post, CNAM is described as a way to identify callers before picking up. The Caller ID wiki page also describes incoming Caller ID name lookup as an optional per-DID setting that can display a caller name for US and Canadian callers.

That is helpful! But identifying a caller and filtering a caller are not the same thing.

There is also a VoIP.ms Community Forum thread where someone asked for exactly this: blocking repeated callers by CNAME/CNAM because the caller used a pile of different numbers. A VoIP.ms staff reply said the feature had been suggested before and that there was no ETA.