Police officers are not going to be walking down the street asking people for papers. If you call the police to report a crime, they are not going to request you to prove legal status due to that. (Calling in a crime does not give them reasonable suspicion you're an illegal alien).The Arizona Immigration Law copies federal code already in place and moves it to the state level to allow police the ability to detain, arrest and try transfer illegal aliens or to transfer to ICE. There is nothing "new" in the law, other than it's at a state level now.
if you are stopped for speeding and can't produce your driver's license, then there is a reasonable suspicion that you are here illegally.. but you CANNOT be stopped just to check if you have papers..