Consumer Reports, which claims the largest nonprofit educational and consumer product testing centre in the world, still cannot recommend Apple's iPhone 4 to consumers.
The news comes after Apple announced it would end the free Bumper case scheme at the end of the month.
Apple announced: "We now know that the iPhone 4 antenna attenuation issue is even smaller than we originally thought. A small percentage of iPhone 4 users need a case, and we want to continue providing them a Bumper case for free."
"For everyone else, we are discontinuing the free case program on all iPhone 4s sold after September 30, 2010. We are also returning to our normal returns policy for all iPhone 4s sold after September 30. Users experiencing antenna issues should call AppleCare to request a free Bumper case."
Apple's decision has not pleased the customer advocacy group. "Apple provided no data to detail its claim of lower-than-expected incidence of dropped calls with the iPhone 4," Consumer Reports notes in a blog post on Monday.
Consumer Reports previously found in tests reception problems could occur when a finger or hand touches a spot on the iPhone's lower left side, especially if the phone is being used in an area with a weak signal.
"In his July 16 news conference announcing the free cases, Apple chairman CEO Steve Jobs said the iPhone 4 dropped only about one call per hundred more than its predecessor, the iPhone 3G S, which remains available."
"Jobs also then reiterated the company's earlier claim that all smart phones have similar problems, and that 'no one has solved this problem.'"
"Our tests found the Bumper successfully mitigates the iPhone 4's reception issue, which was a weak point in the phone's otherwise-stellar performance in our tests," Consumer Reports continues.
"And we agree with Apple that not all iPhone 4 owners will experience reception difficulties with the device. But putting the onus on any owners of a product to obtain a remedy to a design flaw is not acceptable to us. We therefore continue not to recommend the iPhone 4, and to call on Apple to provide a permanent fix for the phone's reception issues."
Founded in 1936, Consumers Union (CU) is billed as an expert, independent, nonprofit organisation whose mission is to work for a fair, just, and safe marketplace for all US consumers and to empower consumers to protect themselves.
CU publishes Consumer Reports, which claims to be one of the top-ten-circulation magazines in the US, and ConsumerReports.org, which reportedly has the most subscribers of any site of its kind.