I upgraded from a 3g, I cant recall any dropped calls. I have had my iPhone4 since launch date, I purchased a $15.00 Rocketfish case from Best Buy 2 bays before the phone arrived, and hasnt been off the device since.
I did peel the case off to test for antenna attenuation, and only lost 1 bar pre/post the I0S4 update.
🙂