In the movie The Bourne Supremacy, ass-kickin' hero Jason Bourne is in the CIA's sights. He let's himself get captured, knocks out a field agent, clones his SIM, and puts everything back in place. So when the agent wakes up, he doesn't know any better. When he reports Bourne's escape, Jason is able to listen in with his cloned SIM, gaining more info about his enemies.

Ok, that entire sequence has its "only-in-Hollywood" qualities. First, it would take longer to clone a SIM, not the few minutes that Bourne had. And SIM cloners hardly do it because they're playing the games spies play; they just want free calls at your expense.

SIM cloning is basically copying the data on the SIM so that you can pretend to be the victim, meaning all your calls will be billed to him. At least that requires physical access; with older phones, intercepting radio signals was enough! So, preventing SIM cloning is easy, all you have to do is make sure no one else is left alone with your SIM.

So Here's a Word of Advice: When you have your GSM or UMTS (these devices use USIMs) smartphone or PDA phone fixed, make sure to keep the SIM. The technicians have their own SIMs to test the gadget anyway. You never know, someone in the back might clone your SIM while the people out front work on your phone.

Something to Scare You More: It's so easy to clone a SIM that you can download instructions to do so.