My Verizon iPhone 4 signal is much more robust than my former AT&T iPhone 4 signal was (in most places), but it's difficult to tell if this is due to the drastic change in antenna layout or just Verizon's (subjectively) better reception.Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_6 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8E200 Safari/6533.18.5)
Like I said I WISH I was paranoid , it's possible that it happens to you and you just don't notice . If you have 4 bars chances are your dropping to 2 or 3 in which case it doesnt matter. I latterly thought people making these threads were crazy and now here I am. Do you use a case? Are you on AT&T or Verizon? Like I said earlier you don't even need to squeeze it to can just set it in your palm.
I found this anandtech article really helpful in understanding a little bit about how the Verizon iPhone is designed and how it differs (2 antennas etc) from its AT&T brethren. Unfortunately it will not alleviate any issues you are experiencing, but it may help you to put it in context.
http://www.anandtech.com/show/4163/verizon-iphone-4-review/2