How did Hollywood so quickly cobble together last Friday's unprecedented TV event, "America: A Tribute to Heroes"? In it's latest cover story, on how stars are helping America in this time of crisis, PEOPLE reports that preparations for the show had kicked into gear only six days beforehand. The heads of the major TV networks hatched the idea of a joint production and contacted producer Joel Gallen, 42, who'd done the MTV Movie Awards. Envisioning a show "about healing and hearing the message of the songs," he called Paul Simon, who quickly signed on to sing "Bridge over Troubled Water." Mariah Carey agreed to do her first performance since her second hospitalization for an emotional breakdown. "I called her manager and said, 'I don't know where she's at mentally, I just want to know if she would come out and sing her song 'Hero,' " says Gallen. "Her manager called her and she was very emotional. She said, 'I have to do this.' " Musicians and actors rushed to volunteer; within 24 hours the show was on its way to being overbooked. (Sources say even Michael Jackson was turned down.) "Too many people wanted in," says Gallen. "By Tuesday I was asking myself, 'What do I do with all these people?' " Enter George Clooney, who suggested a celebrity phone bank that would give more stars a way to play a part -- and surprise a few donors. "One caller didn't want to talk to me," an amused Reba McEntire told "Extra." "They wanted to talk to Jack Nicholson, so I said, 'Well, I'm sorry. He's busy talking to somebody else.' "