Some sad individual decided that he would use some simple
microelectronics mounted on a rubber
tube to make
condoms that played a particular
tune during the ... um ...
act.
The electronics side is not too complicated; being pretty much the same as the technology used in musical greeting cards. There has also been a lot of humour about which songs such condoms should play.
Urban legend? Well, try this:
http://www.memailorder.com/musicalrng.htm