Two RVs hit head on - Hwy 49 in California

Some laws are written and passed more as a result of public pressure and political expediency without much thought given to the law's enforceability in the real world, and some "texting while driving" laws fall into that category. It's not uncommon for texting while driving laws to not specifically prohibit a driver from holding a device, looking at a device, or even using the GPS or other functions of the device, thus making it difficult for an officer to base a traffic stop (let alone a citation) on simply seeing a driver looking at or even operating a handheld device even if it's considered a primary violation in that jurisdiction. Where those legal exceptions exist, the officer has to somehow be able to prove they were texting at the time. In the real world, those laws with problematic proactive enforceability issues are more typically enforced after the fact (crash investigation, etc) if it can be proved that the driver was in fact texting at the time.

Of course, some jurisdictions already had blanket "distracted driving" laws dating back long before the existence of cell phones, which render specific texting-while-driving prohibition needless. However, depending on the judge, the officer typically needs specific behavioral indicators (swerving, crash, etc) or other incriminating evidence of distraction to gain a conviction.