UK PSTN Switch Off Begins: How Will It Impact Your Business From 2020 onwards you are no longer be able to purchase integrated services digital network (ISDN) and public switched telephone network (PSTN) circuits in the United Kingdom. As of 2025, the PSTN circuits will be shut off completely. This is a major step towards the United Kingdom’s mass IP-network migration, with VoIP core networks set to replace all of the outdated legacy technology. What is ISDN? Integrated service digital network (ISDN) is the first iteration, launched years ago, of high-speed internet. ISDN first appeared in the 90s and revolutionised internet connectivity. Many credit the technology as being the groundwork for modern, faster internet solutions. What is PSTN? The public switch phone network (PSTN) is what you might refer to as the classic analogue telephone system—the system that enables landline connectivity. This centuries-old technology was introduced during the 1800s and allows ...