This is the same kind of vintage 'Grillo' (Italian word for cricket) telephone that was used by the IMF in many of the later episodes. These rotary-dial telephones were made in Italy starting in 1965. This one has a 1968 date stamp. They get their name from the 'cricket' sound of the ringer. The design was considered to be revolutionary for the time due to it's shape, small size, and innovative design features. The Museum of Modern Art has one of these Grillo telephones in their collection.
