The uproar over the iPhone 4's call reception, and Apple's suggestion that users slap a case around their new phone, has delayed shipments of the company's own "bumper" casing and driven up prices on eBay.

Reports of call and data signal strength problems in the new iPhone 4 first surfaced last week, but continued to gather momentum Wednesday as the technology site AnandTech published test results that quantified the signal loss, or attenuation, when the iPhone 4 is held in certain ways.

Last week, Apple acknowledged that holding the iPhone 4 may result in a diminished signal that could make it difficult to make and maintain calls or retain a data connection. Among its suggestions: Buy a case .

"Avoid gripping it in the lower left corner in a way that covers both sides of the black strip in the metal band, or simply use one of many available cases," Apple said in a statement last Thursday.

Apple's recommendation may have resulted in the delivery delays Apple is now reporting for its own "bumpers," a strip of rubber and plastic that fits around the edges of the new iPhone.

According to Apple's online store, the basic black bumper ships in five to seven business days from the time it's ordered. Other colours -- iPhone also sells bumpers in white, blue, green, orange and pink -- won't ship until July 16, more than two weeks away.

Savvy entrepreneurs have taken advantage of the bumper shortage to jack up prices on eBay, with some entries posting prices several times higher than the $29.99 Apple charges.

One eBay entry first noticed by the Apple enthusiast site 9to5 priced a white bumper for $99.99, more than three times Apple's list price .

A search of eBay for "iphone 4 apple bumper" returned more than 80 entries, ranging in "Buy It Now" price from $39.99 to $99.99. As of 4 p.m. ET, one black bumper up for auction had been bid up to $51 .

Some of the listings call out the iPhone 4's signal strength problem as a part of their marketing pitches. A $69 blue bumper , for example, links to a story about the study.

iPhone case maker and seller Case-mate said sales of its iPhone 4 cases have been brisk, but was unable to tell whether any part of that upswing was due to the antenna issue.

A case is the best way to reduce any signal loss caused by holding the iPhone 4, an antenna expert said today.

"Will a case help? Yes," said Spencer Webb, an antenna engineer with 11 patents to his credit, and the president of AntennaSys , a mobile device antenna design and consulting firm. "Will it solve all the problems? No. But I can't imagine carrying an iPhone without a case."