When Minnesota governor Tim Walz signed the “hands-free while driving” law April 12, it meant Minnesota joined 17 states in requiring drivers to have their cellphones in hands-free mode while driving vehicles. It also gave people months to prepare for the day that they wouldn’t legally be able to hold their phones in the car.

But now it’s showtime — the new law went into effect Aug. 1. Under the new law, drivers can use their device in hands-free or voice-activated mode only. That means manually punching in an address or a phone number while driving is not allowed. Talking on the...