These telephones are now 50 plus years old plus. They used a huge amount of resources to make them.They were designed as a rental item, to be refurbished and sent out to the next customer, for as many years as was possible. They were built to last and to work as perfectly as possible. If you think about it if an engineer was sent out to repair one it was a cost to the GPO. The parts were made to a fantastic quality and were designed to be totally interchangeable. This means if you strip parts off a dial it will fit perfectly to another. The parts were made to very close tolerances and the GPO were very careful to keep up their standards. This is why so many survive and are still working perfectly today. Try to think of any other electro mechanical item that can still be used today as it was intended 50 to 80 years ago. It is a terrible waste of resources when even one of these amazing items end up in landfill. I believe they have many years of use left in them and even when the new Voip systems are introduced, they will work perfectly. They have minimal modern resources added, such as a new line in Braided handset cord, an electronic microphone and maybe a pulse to tone unit. Buying a telephone fully restored will still outlive any modern throw away item mass produced today. Modern mobile telephones are designed to last on a couple of years and if anything goes wrong after warranty they cannot be fixed. This is because the makers want you to buy a new one and so link parts with coding etc to prevent replacing parts. I think this is criminal and should be stopped, but that's for another rant. See Louis Rossmann on YouTube to view his efforts to enable a right to repair law in the USA.