I'm not going to say it's the perfect solution or answer, but what other one can you come up with? You can pass a hundred laws against cell phone use and texting but people will not obey them if there's no (or a slim) chance of them getting caught. They don't think it's any worse of an offense than speeding. Everybody does it, only a small minority get pulled over. It would depend on the range of the jammer. Seems to me that would increase out of doors due to line of sight being longer. They're obviously not paying attention now so how much worse can it be? Probably work best in rush hour, bumper-to-bumper as opposed to open traffic on an expressway, but still. And if I can annoy just a few of them... Just a thought. I don't have one, but I keep thinking about it (jammer, not thought!)
I wasn't saying I had a better solution, I was asking if the solution you proposed actually had the results you were looking for. I don't believe it actually works out that way.
We're all frustrated with the situation, and human nature is to want to do something rather than nothing. I just don't see this having the intended effect, but actually making the situation worse.