The peer-reviewed studies that say cellphone use (even hands free) is equally or more dangerous than drunk driving leads me to say this law is worthwhile.

http://www.nsc.org/learn/NSC-Initiatives/Pages/distracted-driving-research-studies.aspx

"Understanding the Distracted Brain: This NSC white paper examines why driving while using hands-free devices is risky
AAA Foundation for Traffic Safety: Research shows that voice-activated in-car technologies dangerously undermine driver attention
Voice-to-text offers no safety advantage over manual texting, says a study conducted by Texas A&M Transportation Institute"