There are at least three bands & one artist associated with this name. 1) ATP are two trance producers from Deinze, Belgium. Their names are Thomas Hendriks and Andy Sergeant.
Started only one year ago with producing, their track "Driftations" is already played by Armin Van Buuren on his radioshow. These trance producers have a great future before them. You can find more about them on their website: http://www.atpmusic.be
2) ATP can refer to a Japanese rock band.