I recently discovered that calls from certain phones (like one particular line from my employer, and another from a vendor) don't make my mobile phone ring. From the caller's perspective, the destination phone does not ring - it goes straight to voicemail. From my perspective, there is no ringing and no missed call; the only way I know they called is if they left a message (I'd get the voicemail). This was 100% repeatable from that extension, and I had a good signal and could make calls on my mobile at the time.
The exact same calling number had the exact same result on a co-worker's phone (but calling an AT&T phone from that number worked). Mine's Android and theirs is Apple, so it has nothing to do with the make or model. On mine, "Filter spam calls" is off, there are no blocked numbers, and "Block calls from unidentified callers" is turned off. I do get calls from numbers not in my phone book, including spam calls (even ones specifically marked as probably spam), so there doesn't seem to be any kind of blocking on my phone.
We managed to get it working correctly from the employer extension - the outgoing CallerID was set to the internal extension number instead (like 51234). Changing it to the full phone number including country code (like +1 234 567 8901) didn't work either (despite using a valid number). Only setting it to 234 567 8901 (no +, no country code) would allow the Verizon phone to ring.
Verizon, please allow calls to go through even if the CallerID isn't in your preferred format, or even a valid number.
