If you've ever needed to identify a song that is playing somewhere around you, you've probably already used SoundHound or Shazam which both listen to your surroundings and pop up the best guess - usually right on the money.
The two apps are pretty similar, though they obviously use different algorithms, so I always keep both on my phone just in case. Additionally, SoundHound recognizes humming and whistling, which makes it even more valuable.
While the free version of Shazam allows only 5 IDs per month, SoundHound went unlimited in their basic app a few months back. So, why would anyone use SoundHound Infinity then, a $5 app that is free in the Amazon Appstore today, when they could identify an unlimited amount of songs for free?