The safest precaution that you can take when using cellular phones while driving is:

Question

Minors may not use a cellular phone while driving, except for certain emergencies. Cell phones are allowed to be used by drivers over age 18, but a hands-free device should be used.

Accepted Answer

To use hands-free devices so you can keep both hands on the steering wheel.

Answer

To keep your phone within easy reach so you won't need to take your eyes off the road.

Answer

To review the number before answering a call.