Mobile Phone Jammer

I know that to interfere with a phone signal you would have to transmit your own signal at the frequency a mobile phone operates on. I was wondering how you would produce noise in a circuit, and upconvert it to the frequency the phone works on.

What are you trying to do? diable the mobile phones in a given vicinity? I know that there are such commercial devices used by some "up-class" restraunts and cinemas so that they dont have to ask people to switch off phone! is this what yer tryin to do?