In Germany, the "Deutsche Bundespost" had a monopol on selling telephones. The modell of the 50s and 60s, made of bakelit, is the modell "W48". In the 70s, it was replaced by the gray "FeTap".
Many of them are sold on ebay for decoration purposes. But using cheap chips and modules, they can become a modern wireless phone, either a GSM-Mobilephone or a DECT device.
Thats what I did. PCBs are manufactured, some components ordered for 50 bucks and quickly soldered, and after crimping the cables, the original historic stuff is easily replaced. I added some senseless but funny features like an internal MP3-player to have some more fun with it.

State of the project: the GSM versions, both W48 and FeTap 612, project is finished. the design matured to kind of a professional state, plans and code are available on github now.
The DECT variants are still under development. It turned out that bringing DECT modules to life takes some patience. Unfortunately, I decided to use a module which is not available in smaller quantities. Maybe I have to restart this project almost from scratch if I need to use another module which is available at farnell and mouser.