IPhone 4 loses reception when you hold it by the antenna band
gizmodo.com
gizmodo.com
This seems pretty serious design flaw. Usually antennas are placed in the way that normal holding position doesn't interfere with them too much. In addition, antennas should be insulated. Probably a thin layer of insulating material would help in this case too.
Simple explanations are always the best. Now, time to sell my 3GS.
Man goes to a doctor. Says, "Doctor, it hurts when I do this." (Holds up arm as he explains.)
Doctor responds, "Simple cure: Don't do that."