So a logical choice on the smartphone would be that application that shows the license to the officer should be done without the need to sign on to your cell phone. This would need to be done so no officer violates the "no access to phone, without a warrant"

Then if you have to give your phone to the officer so he/she can return back to the auto to do some more investigation, who is going to pay when the phone is returned and it doesn't work.

Not a good idea of exposing any of this in the "field".

Maybe allowing the license to be scanned in a building or something like that.

Needs to be though out more.