This is unusual to find and so I would rate as a collectible of the future.
This was made for BT by Northern Telecom UK. Customers would have had to pay a purchase fee and rental. Needless to say not a common item. This is actually quite a heavy well made telephone. It has an adjustable metal mechanical bell inside and is designed to get noticed. I have stripped it down and given it a good clean. I fitted a new line in lead and gave the internals a good dusting. I have fully tested it for dialling out and receiving calls. It has some colour fade and I have cleaned the cord the best I can and so looks very good. Don't expect it to look as new but it is a very nice telephone.