The liner notes are quite extensive and Quincy Jones discusses Bono's participation:

One night in 1987, Charlie Hicks called from the limo and said that he was "With someone that wanted to meet me."  "Tonight?" I replied, but before I could get the rest of my sentence out he said he'd be right over and hung up the phone.  Five minutes later, Charlie, Bono and his lovely wife Ali walked throuh the door.  He told me how he had listened to my albums growing up.  I have to confess I didn't know anything about U2, but four hours later, there we were still talking.  The next night, Ali picked me up and brought me to the Los Angeles Coliseum.  Our seats were center stage right near the soundboard.  I became an immediate fan.  Later, during the Rattle and Hum tour, Bono leased the house next to mine.  We've been friends ever since.  He is smart, perceptive, curious, warm, real and strongly connected to music's roots.  His introduction of Sinatra at the Grammy Awards was so on the money that I asked him to send me a copy of it.  He is the perfect fit for the middle of this.  The addition of Bono simply felt natural, the way things should be.

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