Apple Inc.'s (AAPL) iPhone won't hit stores until Friday, but the heavily hyped gadget already has unleashed a cottage industry of touch-screen protectors, leather hip carriers and car adapters.

Even the most enthusiastic manufacturers said creating formfitting iPhone accessories was an enormous challenge.

A notoriously tightlipped Apple kept many partners in the dark on precise specifications, and some of the company's most trusted accessory manufacturers still have not touched a genuine iPhone.

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To compensate, many cribbed size and weight specifications from Apple's Web site, then created models out of wood, cardboard or plastic. They shipped models to Apple for advice on whether headset and other outlets were placed correctly. They adjusted and resent revised versions to Apple.

Many made educated guesses about curved moldings or the location of the proximity sensor, which turns off the touch screen when near the user's face. A one-millimeter error could result in headsets that come unplugged or an uncomfortably hot screen.

"The engineering aspects were a huge challenge," said Marware Inc. sales manager Sean Savitt.

Hollywood, Fla.-based Marware, which sells iPod accessories in Apple stores and on Apple.com, assigned an industrial engineer to build a molded-plastic custom prototype that weighed precisely as much as a real iPhone.

Marware sent the model to Apple for comments — but it's unclear how many of the roughly 300 Apple accessory makers had similar access.

"There are a lot of manufacturers' cases that are going to have some fundamental mistakes that will only be revealed after launch," Savitt said. "There was a great deal of information to process and a great deal of guesswork."

Cupertino-based Apple did not respond to requests for comment.

The company recently sent some partners a memo urging them not to talk to journalists or rivals about marketing strategies — including whether their accessories would be on sale alongside iPhones. Partners are not supposed to issue news releases or advertisements until after the launch.

Digital Lifestyle Outfitters Inc. will have two cases available in AT&T Inc. (T) stores starting Friday. The phones are slated to go on sale at 6 p.m. local time Friday at Apple and AT&T stores, and on Apple's Web site.

Immediately after Apple Chief Executive Steve Jobs announced the iPhone in early January, DLO developed rough models in balsa wood based on the general specifications he gave out. Engineers then built plastic replicas with glass touch screens.

Even the slick photographs of the iPhone HipCase and Jam Jacket on DLO's Web site use model iPhones, said Andrew Green, vice president of marketing at Charleston, S.C.-based DLO.

"We didn't have a lot of special details initially. Apple shared stuff with us, but not exclusively," Green said.

After the January unveiling, several partners said, Apple cut off access to its designers Web site. Apple may have been making last-minute tweaks — a common practice in the electronics industry, where products have short life cycles.

"At one point they weren't going to make the specs available to any vendor until the launch. We all just gasped," said Carrie Scharbo, co-founder and vice president of Cumming, Ga.-based Case-Mate Inc.

Case-Mate, which began manufacturing cases at its factory in China after receiving final specs from AT&T May 22, plans to sell a patent-pending, impact-resistant iPhone shell with an injection-molded inner sheath.

"To build a sleek and slim design without all the specs is challenging, but that's our schtick," Scharbo said. "The nerve-wracking thing about this one was that everything was so hush-hush. We felt fortunate that we could partner with AT&T."

EBay Inc. (EBAY) listed roughly 1,700 iPhone accessories Wednesday, from belt clips to whimsical T-shirts proclaiming "I (heart) my (picture of iPhone)," many of them from obscure makers.

The San Jose-based auction company is anticipating numerous auctions of iPhones themselves. Instead of signing up for cellular service at the time of purchase, iPhone buyers sign up through Apple's iTunes online store, making the phones easier to give as gifts or resell.

About 2,000 eBay security representatives are scheduled to be on the lookout this weekend for iPhone scams.

But Cat Schwartz, the eBay executive in charge of electronic gadgets, acknowledged that she can't do much about ill-fitting accessories.

"It's premature for people to be putting out accessories," Schwartz said. "Until the unit comes out, I wouldn't advise people to buy a bunch of accessories."