Flashing your virtual headlights

It's not as common a practice as it once was, but if you drive in the US, you've probably heard of the custom of flashing your headlights to warn oncoming traffic of a speed trap you've just passed.

Now you can do the equivalent on the web, using your cell phone. Once you've set up Trapster, you can speed dial a phone number (without taking your eyes off the road, assuming you're good at speed-dialing) to report a speed trap you drive past. Other Trapster-aware drivers will then be alerted as they approach the trap. You can also go online (while parked, presumably) to see speed traps in your area.

Is it legal? It seems like it ought to be, particularly if it's a passenger and not the driver playing with the phone. It's not clear that The Man minds all that much either, the question being whether The Man is more interested in getting you to slow down or in handing out tickets.