If I could get a bluetooth handset that worked great as a one-handed receiver, with no more than an on/off-hook button, and big enough to reach both my ear and my mouth, I would keep my smartphone in my pocket and use the handset.
Thing is, no such device exists. There are headsets and bluetooth earsets, but both require excessive fiddling, and the earsets don't even work if you have a bushy beard and a deep voice. I *miss* being able to just pick up the receiver and talk, without having to yell because people can't hear me.
And yes, I mostly use the smartphone as a PDA. Because, quite frankly, it sucks at being a phone. So much so that I'll get up and walk to the landline when I need to make a call. My cell phone phone usage has averaged around 2 minutes per month.