iPhone 4's now infamous antenna glitch may be yielding a bumper crop of windfall sales for Apple. The company appears unable to keep up with demand for the so-called bumper that supposedly mitigates the problem.

Apple's online store shows the black version of the bumper is on a five to seven day back order, while the wait time for the white and color versions, including pink, blue, green, and orange, is three weeks.

The bumpers are priced at $29, so if even a minority of the millions of consumers who've purchased an iPhone 4 since the product was launched last month shell out for what's become a virtually mandatory add-on (if users want the device to work properly), Apple stands to gain a substantial amount of additional revenue from iPhone 4's design flaw.

Many iPhone 4 buyers have said the signal falters if the device's bottom left corner is covered by the palm of one's hand—a situation common if it's handled by lefties. Reports suggest the problem arises because grasping the phone in such a manner covers a small gap that's meant to separate the two ends of iPhone 4's perimeter antenna.

The bumper, which wraps around the phone's exterior, works by insulating the antenna from human contact. Some watchdog groups are calling on Apple to provide the bumpers to iPhone 4 buyers at no charge.

"Apple suggested owners mitigate the problem by holding the phone differently or purchasing a case. But those solutions put the onus on consumers and skirt Apple's obligation to offer a product that works consistently and reliably out of the box," Consumer Reports staff said in a blog post Tuesday.

"We think it's the company's responsibility to provide the fix," the blog said.

Apple may yet cave in to the demands. The company has scheduled a press conference for Friday to provide an update on the iPhone 4 antenna issue, and some are speculating that it will announce free service options for the device, or even a recall.

The network plays a critical role in the success or failure of your unified communications deployment. We tell you how to build to win. Download the new issue of Network Computing for this story and more. Download it now. (Free registration required.)