Wasn't there a movie by that name about that very thing?This doesn't actually relate to Christianity at all which is why I posted it here.
Numbers stations are shortwave radio stations that broadcast these voices that recite what sounds like random numbers, and the numbers are apparently codes. They have been around since World War I. And they say the broadcasts don't mean anything except to the person sending and the person receiving them. Apparently if you have a shortwave radio you can tune them in and hear them. I listened to a few clips from YouTube and downloaded some recordings of them, they are quite eerie and creepy. And it's a little unsettling to think that they are used by spies.
Here's an example of one, this starts with a xylophone melody and then is a series of random numbers spoken in German in a little girl's voice.