This Model 56 telephone is the specific phone that first came out in 1956 for the national phone company of Belgium, Régie de Télégraph & Téléphones (RTT). This model saw production until 1966, lasting just over a decade. Two different companies manufactured this telephone model for the RTT: the Ateliers de Téléphone et Electricité Anversoise (ATEA) and the Bell Telephone Manufacturing Company (BTMC). The full model number on the bottom of the phone reads RTT-56-B, with the B indicating that this phone was made by the BTMC.
This particular phone is all black (one of the two available colors, the other being in white), and has a brass handle for carrying. The brass rotary dial in the middle is a black and white art deco style design. The body and handset are both made from Zamac (a more robust zinc alloy). While bakelite plastic was a popular material for phones at the time, all RTT-56 phones were made from Zamac.
Some inconsistencies on this phone suggest that either modifications were made, or the authenticity can be called into question. When people replace their phones in Belgium, RTT would often send the old phones over to the USA as it was not uncommon for people in America to modify them. This phone as a large black button in the front instead of a small white one, which the RTT-56-B would normally have. Additionally, neither a lion nor a RTT logo is found on the front - instead it has a decorative gold writing on the side that reads "Bilgique Bell Telephone MFG Company". These modifications were seen as commonplace on this model phone.