The fix for this is easy: pull people over. When I was a teenager, cops met their quotas by watching for people with a phone (back then folks were talking, not typing). This is a big part of what drove people to get bluetooth earpieces: you wouldn't get pulled over for having one and talking on the phone (and cars didn't have microphones yet, so there wasn't another option).
People will be pissed that they're getting pulled over for using their phone while driving. But if there's no expectation of punishment for breaking the law, people will continue breaking the law. And texting and driving is breaking the law. And if I can spot half a dozen people texting and driving on my way to the gym, cops can definitely spot folks texting. Hell, if I could apply for the special cop job of "pull people over for texting" and nothing else, I'd do it purely out of resentment for distracted driving.