On Merseyside the Police have started using 'spies' (usually standing in bus shelters) to watch for passing motorists using mobile phones. This is mainly during the rush hour. They call ahead to a patrol car who will pull you over. Maybe this is being done elsewhere, but I have only just found out after a friend was pulled over.
I don't think this is a bad thing by the way. If it helps to save lives, then all well and good.