"The Verizon iPhone 4 has a problem that could cause the phone to drop calls, or be unable to place calls, in weak signal conditions, Consumer Reports engineers have found in lab tests.
The problem is similar to the one we confirmed in July with the AT&T version of Apple's newest smart phone. It can occur when you hold either version of the phone in a specific but quite natural way in which a gap in the phone's external casing is covered. The phone performs superbly in most other respects, and using the iPhone 4 with a case can alleviate the problem."
Consumer Reports Electronics Blog: Verizon iPhone 4: Mind the gap, our tests show