Motorola's low-end 911 phone system, Emergency CallWorks (ECW), is Asterisk with proprietary modules running on Linux under Proxmox. Granted, Motorola is killing the produce, but it's out there. The one I babysit is heavily firewalled but I'd imagine not all of them are.
That is not the core, however; the core means the central pieces of a large telecom, the part that handles all the needed data to set up say, 10,000 or more calls per second.
For sure. The implicit trust that participants on the PSTN appear to give to each other, imparts a certain amount of undue influence to the constellation of dodgy systems interconnected to it.
No, but plenty of businesses that process your call data, whether it's for call recording, transcription, IVRs, speech analytics, CRM integration, call queuing, auto dialing, or SMS/chat features, are liable to be running stuff like FreeSWITCH, Asterisk, or similar somewhere in their stack.
Any business with a PBX that wants to do more than just basic call routing and PSTN connectivity is likely using third party tools. And a significant number of those tools are built on FreeSWITCH, Asterisk, or similar.
