As a person who drives a lot for work and has to be always available to answer a phone call, I do use my cell-phone A LOT while driving. Texting while driving is the worst idea ever especially with touchscreens - a person actually needs to look at what he or she touches. I, personally, miss calls and don't answer texts (thank Android for speech recognition) if it is not safe.
I also can see why law is in place. Mostly because of teenagers who don't have proper driving skills but possess texting addictions.
A sandwich is a handheld device but nobody is banning food in the vehicles. They should. Some people would benefit from that.
Use the cellphone or not while driving it is always your judgement call.
If mathematically you end up with the wrong answer, try multiplying by the page number.