The passenger that texts for the driver because they obviously shouldn't be texting & driving. This is especially helpful on a road trip, when you are behind the wheel for long periods of time.
I (a female) was driving on a very long trip & my sister was texting me. I asked my husband to answer her. He sent the reply and after several texts were exchanged he told her l was driving & that he was the cotexter for me so she would know.