Virtually every building in the UK, let alone business, residence and institution requires fixed line telephony services installed by a Telephone Engineer. Besides making and receiving telephone calls this can be for a whole multitude of applications including broadband, fax, intruder alarm , fire panels, emergency lift, backup modems, EPOS, PDQ, door & gate access, PBX.
Since the breakup of British Telecom, its subsidiary Openreach, responsible for the comms infrastructure in the country, are no longer interested in internal issues. Simply if you have a fault it can be a nightmare if you dont have a Plan A.
There is an abundance of telephone engineers with an IT or electrical background who will purport to know this field but there is a dire shortage of independent time served telecom engineers with decades of this experience.