I usually take out the phone and put it on loudspeaker mode if im alone in the car. Otherwise, I dont pick it up and check at some traffic signal/ stop and call that person after I reach home/ office.
I followed an innovative practice of using the cell while driving. I stuck a 1 inch by 1 inch strip of 2 sided tape on the center of my steering wheel. And stick the phone on it. When it rang, i would simply press the loudspeaker button and talk normally. Since it was at my chest level, no problem in hearing or being heard. I stopped this though since my steering had got a bit sticky and messy.
