It looks like it's still true. Here's what CNN has to say about it:
Accessory Makers Zero In on iPhone
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.
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. (Watch people lined-up outside NYC's Apple store waiting to be the first to own an iPhone )
"The engineering aspects were a huge challenge," said Marware Inc. sales manager Sean Savitt.
Of course, the NSFreePublicity object might require that the measurements detailing the locations of buttons and speakers and microphones and SIM trays and whatnot be kept secret for six months after iPhone was announced and before it was shipped.
Somehow I suspect that this is an indication that Apple still has some lessons to learn about partnership.