“Smile” was a song developed for 2004’s How to Dismantle an Atomic Bomb.
“Smile” was actually released in 2004 as a set of demo recordings included with The Complete U2, a digital ‘box set’ released at the same time as the album How to Dismantle an Atomic Bomb. In that set “Smile” is listed as being from the sessions for How to Dismantle an Atomic Bomb. In a digital liner note The Edge speaks about some of the demo tracks:
Every U2 recording session produces its share of unfinished ideas. Some like ‘Smile’, from the sessions for How to Dismantle an Atomic Bomb, just arrive too late. Others like ‘Love You Like Mad’, from the sessions for All That You Can’t Leave Behind, get lost in the crush. There are songs like ‘Beautiful Ghost’, from The Joshua Tree demo sessions, and ‘Flower Child’ from the All That You Can’t Leave Behind sessions that are waiting for a rewrite before they can be finished. Songs like “Levitate’ from the All That You Can’t Leave Behind sessions which just don’t fit in. Wherever they come from, these ideas are often the most revealing of their time, because they are the least worked on songs and recordings. For this reason, they are often some of my favorites.