Gwen Stefani talks about the song Prince and No Doubt worked on.
http://www.dotmusic.com/n...s22111.asp

Here are the relevant parts:

Although the Dre track 'Wicked Day' hasn't made the album, the Prince track 'Waiting Room' is one of the album's standout tracks that, in the notable absence of guitars, tears up the rulebook with an unorthodox structure, an abundance of unusual effects and a classic Prince harmony.

"Prince called me up and asked me to sing on his new record. He flew the whole band out to Paisley Park and the whole thing was if I did this he'd do anything for us. We'd written this song 'Waiting Room' so we sent him the demo and before we'd landed he'd re-written and recorded a whole new demo. We couldn't believe it. He was really fun to work with and really inspired me as far as writing. He gave me a lot of advice."