Consumer Reports says the iPhone 4 has reception problems caused by its antenna design.
After the iPhone 4 went on sale in June, buyers started complaining that holding the gadget a certain way could cause calls to drop.
Apple has said that any phone will lose signal strength when gripped in certain ways. It said the iPhone 4 seems to show a larger drop because it has been using a faulty formula to decide how many signal bars to show.
But Consumer Reports says it tested several phones that use AT&T Inc.'s network, and only the iPhone 4 seemed to have the reception issue.
Consumer Reports says the iPhone 4 will not be marked "recommended" on its updated smart phone ratings list because of this problem.