If you find yourself running into police speed traps often, then you might want to give a new iPhone app a try. NMobile [iTunes link] allows you to locate speed traps, red light cameras, and radar locations. All of these speed detection devices are mapped out on a Microsoft Live map -- this is one of the first native uses of Microsoft Live Maps on the iPhone.
If you are using this application with the iPhone 3G, then you will have the ability to use your GPS location in conjunction with the tracking service from Njection. In "Browse Mode," you can check your area for speed traps, red light cameras, and radar devices. The speed trap locations are submitted by users, and can be submitted through the application (or on Njection's website). Red light cameras and radar locations are also submitted by users, and verified for accuracy by the developers. Speed trap locations are only verified by users.
In addition to browsing for speed traps, you can also be alerted audibly of upcoming traps -- you can find this under "Alert Mode." In this mode, NMobile will tell you when you are approaching a trap, you will also see how many miles ahead the trap is.
Bottom line: this application is solid, but I would like to see a couple features added. For one, you can't get directions in this application like you can in the default Maps app on the iPhone. It would be nice if you could plan a route, and see the speed traps along the way. If you're using this application on a first generation iPhone, you might not get the best experience; however, this can't really be blamed on NMobile; the location data on the GPS-less phones isn't specific enough. You should exercise care and caution while using this application on the road. This application is just a little pricey at $9.99, and is now available on the iTunes App Store.