On April 23, 1913, the International Teleconmmunications Union assigned Mexico the call letter range from XAA to XCZ. However, Mexico did not use this call letter allocation in assigning call letters to the first commercial stations. A list of Mexican stations from 1925 shows one station with an odd call (see 24A). From other sources, this was apparently issued as an experimental amateur call. The remainder of Mexican commercial stations were issued three-letter calls beginning C generally followed by Y or Z. This block of letters was unassigned to any country in the 1913 allocation, but in 1927 the CZ block was assigned to Monaco (the CY block was still unassigned). It should be noted that there are books that claim that a 1924 conference gave the CYA-CZZ calls to Mexico, but I have seen