BT Digital Switchover from PSTN

BT's Public Service Telephone Network (PTSN) is being switched off (this is a global network change). The old copper lines are no longer available to buy as they are no longer sustainable and the equipment (switches etc) which supports the older infrastrucure is no longer available for repairs or replacements. The switch off deadline for businesses is 31/12/2025. However, BT need to know which lines need to be migrated over to Pre Digital Phone Lines (PDPL) where current operating systems etc do not currently work...