Such transmissions are fairly common. They are most often reported in Europe, but can be found anywhere. Each adheres to a strict schedule, and often begin at either the hour or half-after. Most of the time the voice reading these letters is female, though sometimes male or a child’s. Despite being without any obvious function, they seem pretty harmless. So why does no licensed radio station admit to sending them, no government will admit to sanctioning them, and no one will confess to being responsible for them?
According to The Conet Project, a group which has taken to sampling and distributing recordings of these stations, this type of transmission has been observed since World War I, making them one of the first and oldest of all radio broadcasts. With no evident source or purpose for these signals, imaginations have taken reign, and a wide number of ideas have spawned ranging from plausible to tittering-alone-in-the-woods-wacky.
Among the most popular and most viable theories is that the Numbers Stations are a covert means by which government spy agencies use to maintain contact with their operatives. That would explain the need for the official obfuscation of their source, and why the messages are so cryptic; an extremely high level of coding would be required for spies. Perhaps the transmitters must occasionally move as the field agents relocate in the course of their duties.
Another theory is that these are the messages of drug smugglers. They too have reason to prevent unwanted listeners from hearing what they have to say, and there is no reason to think that these operations are less organized than a government job. Some propose that the garbled information is purely disinformation, and if that is the case it is working brilliantly. Perhaps it's just an ongoing joke perpetuated by a small group of malformed senses of humor.
There are also tales of these being messages from those lost in the Bermuda Triangle, or MiB telling each other who to harass, but as tantalizing as such tales are, there is nothing to support them.
In fact, only the theory about communication with spies has ever garnered any official support, and that in the form of the US government accusing the government of Cuba of using the well-known "Atención" Number Station to instruct agents working in the states. The case included having found one of the spies' laptop computers, and the decryption program thereon. With that program they were able to understand the otherwise befuddling messages. Further—if empirical—evidence of this theory is that since the end of the cold war the occurrences of Numbers Stations have greatly reduced.
When a Numbers Station is found there are some diligent souls who take it upon themselves to break out their radio gear and attempt to track the broadcast to its origin, but few are ever found. In the cases where a suspect site is located, no one has been waiting there to claim responsibility. So the search continues.
Article suggested by Panagiotis Angeloudis