Chicago ? Here’s an announcement most concertgoers don’t expect to hear: “Ladies and gentlemen, please turn on your cell phones.”

That, however, is what patrons of the Chicago Sinfonietta are scheduled to hear when David Baker’s “Concertino for Cell Phones and Orchestra” opens the ensemble’s 20th anniversary season Oct. 1 and 2.

“We thought it would be interesting if we reversed what people usually hear at the start of a concert,” says Paul Freeman, the group’s founding music director. The orchestra, which was termed the most racially diverse in the nation recently by the Juilliard School, has been exploring “other avenues of compositions for many years,” Freeman says.

“We’ve commissioned a maracas concerto and a mariachi symphony, and we’ve already had pieces with a great deal of audience participation.”

Freeman says the new work, which Baker is still writing, will probably divide the audience into different sections before cueing them with colored lights to turn their phones on and off. The conductor will control the change in the lights.

“There has to be some degree of organization from the stage,” Freeman says. “The grand finale will probably have everyone playing their cell phones at once. It may be cacophony, but we’re looking at it as being a very adventuresome thing.”