Do it all day every day. I usually use bluetooth unless I'm in my truck because the road noise is so bad I can't be heard through a headset.
As much as many people will argue it, I'm sure if you've been doing it all day every day for years then you're totally fine. I personally made/recieved 54 calls today between 8am and 5pm, many of which I was behind the wheel. I do this every single day and I don't think it affects my driving at all.
We stopped checking for monsters under our beds when we realized they were inside us.