Re:Ask HN: Why can’t I block all incoming calls that aren’t ...
by fyfy18 on Thursday January 31, 2019 @07:47AM
(#19044321)
The whole reason why I did this was because I was playing around with Asterisk and VOIP, and wanted to connect a PTSN line to it (which the OBi device was marketed as), but it turned out I could do everything on the device.
Anyway, at the time I was traveling a lot so had my VOIP number forward to whatever local number I had in that country. That worked great, except on my phone it just displayed my VOIP number as the caller ID, so I had no idea who was calling.
In Asterisk I saw you could set the caller ID, but it didn't work for outgoing calls via my SIP trunk, so I assumed it was disabled by my provider (makes sense). I contacted them, and they said they had unlocked that feature, after which I could make a phone call with any caller ID. I expect there is something fundamental about how the telecom system works that prevents them from blocking these calls, but I'm really surprised at how easy they gave me access to it.
What I've found is that whist it does stop a lot of spam calls they now fake local numbers. Worse they fake them with a missing digit. The phone companies could definitely spot that. I've wondered previously if international telecoms treaties stop the phone companies from acting to block these calls.