Using the magic of Arduino, I revived an antique Bell model 202 telephone and added Bluetooth capability to it.
There are two parts to this. On one end I have an ancient phone from the 1930’s. On the other end, I have one of a dozen “name tags” with hidden LEDs. When a person dials the correct number on the phone, a bluetooth connection is made to a name tag pinned to a person’s lapel. When the connection is made, the phone plays a funny message and the name tag flashes in all sorts of crazy colors.
I documented the “Bell model 202 Bluetooth Telephone” in this Instructable: