In reply to a post by lmschuffer:

...but I was thinking more of those upgrading ( or moving to with a change of provider ) from ADSL or FTTC and so that would already be active and you could perhaps remain with your current supplier for just voice.

If a current provider (or future provider) of an end user's xDSL broadband and PSTN voice account also sells a standalone PSTN voice service (e.g. possibly BT retail?) then it may be possible to cease the xDSL on the line and retain the current PSTN service and number.

However an "upgrade" from xDSL to FTTP and retention of a PSTN service could be problematic - one would have to check with the current or future providers. Alternatively a fresh installation/activation of FTTP (broadband only) whilst the xDSL/PSTN line remains active would allow one to have continuous broadband/voice access prior to transfering the PSTN line to another provider and the ceasation of xDSL.