The Public Switch Telephone Network (PSTN) is aging and will reach the end of life in December 2025. The PSTN supports a number of Openreach products which Communication Providers (CPs) purchase at regulated pricing and often sell to businesses and consumers, wrapped up in their own line rental, broadband and call package deal. These include: Wholesale Line Rental (WLR) and Integrated Services Digital Network (ISDN).

ISDN is available in two common variants: ISDN2 supports channels in pairs and you can have between 2 ISDN channels or 8 ISDN channels. ISDN30 is provided for larger business customers usually, with options to have between 8 ISDN channels and 30 ISDN channels on each service. A single ISDN channel will provide a customer with 1 concurrent call at a time. At the end of December 2025 traditional telephony, including fixed lines and services in the Public Switch Telephone Network (PSTN) will be switched off and withdrawn from service.