I for one do not do anything but drive, when I'm behind the wheel. The people that have my cell phone number, know that if I do not answer when they call I'll call back when I can stop safely. Occasionally, I will take a drink of water from a bottle that my wife opens for me while I drive, but not often. Since I was almost killed by an OBLIVI-TARD I go to great lengths to make sure that I do not add to the problem of oblivious/retarded drivers.
On a side note, I have never gotten a cell phone call that was more important than another individuals life, I can remember when you wanted to tell someone something you called them before you left home or when you got back home. For some it seems that they cannot get behind the wheel without plugging their phone into their ear. Goto the mall and watch some folks, when they get in their car the first thing they do after it is running is get out the cell and plug it in their ear. Ban all of them. When cell phones are outlawed, only outlaws will have cell phones.