I accidentally won a radio contest many years ago in this way. I heard "you are caller 2" and then the DJ hung up. I stayed on because I was confused and then a few seconds later he picked up again and said you are "caller 4". So I just stayed on and eventually said I was caller 10 and the 10th caller won the prize. I assume he was switching back and forth between two internal phone lines.

I was confused because I was calling to make a song request and had no idea that this contest was initiated because they had just played a certain song.