As a rightie, I never hold my phone in my right hand. I always hold it in my left hand so I have my dominant hand free to do whatever I may need to do in middle of a phone conversation (e.g., take notes). Also, when I'm using the device, I hold it in my left hand so I can use my dominant hand to navigate the screen.
I've also made numerous calls from various locals around northern MA in the past few days and have not had any issues with the calls, except at my work/office with its multiple signal blocking walls it might as well be a giant Faraday cage. Though as Nate stated, it's more than likely that my area is just well covered. On a side note, 3G upload speed from my iPhone at my home is faster than my Comcrap cable upload speed.
Speaking of cases, the bumper is not exactly a well-designed piece of equipment.