One known way of fixing the iPhone 4 signal problem is to spend almost $30 on an official Apple [AAPL] Bumper Case. The casing is just a piece of rubber that wraps around the antennae and protects the iPhone 4 from knocks and scrapes.
The guys at Consumer Reports have tested the iPhone 4 bumper to see if it also prevents the signal from dropping. Tests show that it does with the dB level only changing slightly when the iPhone 4 is held.
The video below shows the test being performed along with the explanation of the drop and what they feel Apple should do about it.
In short, Consumer Reports say that Apple should provide a fix... "We're still calling on Apple to provide an acceptable free solution to the iPhone 4's signal-loss problem." We should find out more on what Apple intends to do tomorrow at the Apple iPhone 4 press event that has been scheduled.