Read the law in question, which was from 2009 and amended in 2012. It's made with modern phones in mind, and it was specifically written to combat texting:
As used in this section “write, send, or read a text-based communication” means using an electronic wireless communications device to manually communicate with any person using a text-based communication, including, but not limited to, communications referred to as a text message, instant message, or electronic mail.
Using GPS is not manually communicating with a person. The law does not apply to reading text on a phone in any context other than communications with another person.