What do I need to know? - The technology we currently use to make landline phone calls is due to be upgraded over the next few years, and that means many businesses will need to make a change to their telephone services. Landline phone calls have traditionally been delivered over the old telephone network – this is known as the Public Switched Telephone Network (PSTN). BT has taken the decision to retire the PSTN by December 2025, and to make sure our telephone services continue in ...