As far as enforcing cell phone laws, are you aware of this Oregon Court of Appeals ruling?  I bet the police officers are.  

"In State v. Rabanales-Ramos, 273 Or App 228 (2015), the Court held that merely looking at a cell phone while driving did not violate ORS 811.507. In that case an officer stopped the defendant after observing a light coming up to the defendant’s face in the defendant’s vehicle. The officer believed the light was coming from a mobile communication device the defendant was looking down at while driving.
The Court of Appeals held the officer did not have probable cause to stop the defendant. The Court held that ORS 811.507 only prohibits using a handheld mobile communication device for voice or text communication. ORS 811.507 does not prohibit other uses of handheld mobile communication devices while driving, such as for GPS or listening to music."
How would you suggest the officer get 'probable cause' to stop someone?  I think I know one set of circumstances.