What are SIP Trunks? Lets start with IP Telephony:
IP telephony (Internet Protocol telephony) is a general term used to describe voice and fax using the Internet Protocol. It's used interchangeably with the other mainstream telecoms acronyms VoIP and UC. This form of digital communication is much more efficient and resilient than SS7. The PSTN (The aggregate of telecommunications networks) is moving to digital IP based technologies and by 2025 the PSTN with the United Kingdom should be completely IP based.[1]