We have a live demo on our site if interested - http://speakerblast.com.
We think 4D movies; movies that gets the audiences' devices involved into the experience could be a way of the future. Similar to the texting PSA in China created by Volkswagen (very effective).
That is certainly an interesting idea. I'm thinking, though, that getting it to work and be stable across the many devices we have is prohibitly difficult.
If I were to do something like this, I'd look at the Firefox OS phones. I don't think they are ready yet, but crazy cheap Firefox OS phones will come. They target developing countries, but would also be good for something like this. So when people buy their ticket, you also sell them this cheap device which you've prepared so that it'll work out of the box. It'll be similar to the way they currently sell 3D glasses at the cinemas.
Here's a live demo where we turn a small crowd & their devices into the movie's sound system. http://vimeo.com/71647538
Here's the movie clip I speak of above http://vimeo.com/m/93899424
This is new(ish) type of technology that requires solid and FAST Internet. It may or may not work in various countries based on Internet speeds (10Mbps or higher is recommended ... Possibly 5Mbps of higher could work too. )
Or better yet, if the audience is on numbered seats, print a QR code on their ticket which gives them an URL that includes their seat number as a parameter.