At least several MB a day if you use it a lot. Okay, let's be generous and call it 10MB per day and I use it every day. 31 * 10 = 310MB. This is an 'over the top' calculation making the app's use well within reach of a 1GB plan I'd say.

Note that in the UK, one of the early adopters of speed cameras, they're now being phased out!! The truth of these buggers is that they cause more accidents than they prevent (through sudden braking when the camera is spotted) and are considered a 'stealth tax' on the populace. This app should actually improve road safety if it allows users to brake gently and safely ahead of time. Kudos to trapster.com!

Only one mistake “enable the compass (iPhone 3GS only).”

We use vectors calculated from the direction of travel, like a car navigation system, instead of simply using the compass (which also means it works on the $99 iPhone). The option for map facing North is still available but to change the map to rotate dynamically to your direction of travel, select the top blue “N (with an up arrow)” icon on the right side of the screen.

For more on this, visit Trapster's blog: http://blog.trapster.com