Apple iPhone 4 has been delivered but some users complained that the smartphone cannot connect to the network and drop calls, if they hold the iPhone 4 in left hand.
Apparently, it is caused by the unique design of the iPhone 4, which uses stainless steel band as part of the antenna system. When you hold iPhone 4 with left hand, the antenna at the bottom-left corner is covered by your skin and thus, somehow, block the radio signal.
Anyway, not every iPhone 4 has the antenna problem. Some kind of bad quality control there. If you got the unlucky one, attaching Apple rubber bumper accessory would solve the problem.