The iPhone 4 has had some issues on take off, and Steve Jobs has responded. Many users have complained that the network reception on the phone is terrible and when holding the phone in the bottom left corner, the bars drop to zero.
Cell phones now place their antennae in the bottom of the phone so that the radiowaves aren't radiating near the head. Apple seems to have moved the antennae to the sides of the phone. Stve Jobs says, “You're holding the phone wrong”. Apple's official statement on this is:
Gripping any mobile phone will result in some attenuation of its antenna performance, with certain places being worse than others depending on the placement of the antennas. This is a fact of life for every wireless phone. If you ever experience this on your iPhone 4, avoid gripping it in the lower left corner in a way that covers both sides of the black strip in the metal band, or simply use one of many available cases.