What's higher than the CN Tower? How about playing on an airplane cruising at an altitude of 35,000 feet? That's exactly what Mat Kearny did when he performed on a Southwest Airlines flight, possibly setting an entirely new record for World's Highest Concert while singing into the phone that flight attendants use to make announcements. The Nashville-based Kearny, who is best known for his 2006 album 'Nothing Left to Lose,' later called the gig "cool."