iPhone 4 users have already started complaining about 2 problems.

1. Some users say that when held in a certain position that covers the antennae, the bar signals slowly reduce. Some times when making a call the call drops since the users is blocking the antennae. Some users have filed lawsuits against Apple.
On Friday Apple released a letter saying that there was a problem with the algorithm that would miscalculate the correct number of bars. They also said that all phones held in a certain way can have reception problems. So Apple will soon be releasing an update for the iPhone 3G, 3GS, and 4.

Yellowish Screen. Some say that the iPhone 4 has a yellowish screen or sometimes yellow blotches. It has been confirmed that it is the bonding chemicals that laminate the glass to the screen, and through time the yellowish should go away.