Some national radiation advisory authorities... have recommended measures to minimize exposure to their citizens... Do not use telephone in a car without an external antenna
I'd wager most people take this advice to mean don't talk on the phone while inside the car. However, to me it sounds like the above also implies don't use GPS navigation apps, at least not apps that constantly communicate with the server (e.g. for traffic reports).
Does this make sense? I guess it depends on the amount of data sent to and from the server?