The internationally recognized range of call sign prefixes assigned to Cuba is CLA to CMZ. However, in the early days of broadcasting, Cuba did not conform to this system. The first commercial broadcasting station in Cuba (opening October 10, 1922), operated by the Cuban Telephone Company (a subsidiary of AT&T) was assigned the call PWX. (While this call would today be assigned to Brazil, under the 1912 plan the latter part of the P group was not assigned to any country.) After PWX, a different system was used for all stations: a number (apparently always 2, 5, 6, or 8) followed by 2 letters, similar to what was used for amateur stations at the time in the United States. This system was used for several years (it is known to have been in effect on February 12, 1924), although by 1929, when