If I'm in the computer room I put the phone to my left ear because the phone is to the left of me, if I'm in the kitchen I put the phone to my right ear.
If I'm using my cell phone, I put it to my right ear always
Almost always the left. Unless someone happens to call when I'm doing absolutely nothing. Most of the time I need my right hand free so that I can use it to do whatever it is I'm doing.
It depends on what side of me the cordless is sitting on at the time and which hand I grab it with. I almost always end up switching ears by the end of the conversation, though.