Just because you have a cell phone does not mean that should not observe common courtesy when it comes to others in public places.
There are some times and places where is is not cool for me to hear your cell phone ring. I do NOT want to hear your cell in a place or worship or in a movie theater. Phones should be silenced. And if you forget to silence it, as we all have done, and it rings, DO NOT answer it and hold a conversation. Excuse yourself and go to a more private area. Anything less than that, is a reflection of your home training, or lack thereof.
If you are sitting in a restaurant, I guess it's up to you whether you want to take the call or not. But still, remember the rule of polite society. Recently, while trying to enjoy my meal, I had the pleasure of hearing someone describe, in detail, a horrible rash in a very private area to a medical provider--YUCK!
I realize that we live in the age of technology and I love my Blackberry as much as the next person, but exercise civility!