There was an interesting piece of technology that they actually implemented (I know in at least Japan and France). What you could/can do, is dial a number on your phone, then hold the phone up to whatever speaker was pumping out the tune you wanted to know about. It would then match the song's key features against a huge database (even with shitty cellphone quality), and send you a text message with the answer.
A bit limited, but I've often been in situations where I hear the song that I need to know in the middle of a television ad or film soundtrack or something, useful for that I suppose.
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