By Aidan Malley

Published: 06:40 PM EST

Apple's upcoming iMac has made a tentative appearance in US retail channel systems. Meanwhile, one rumor has the 3G iPhone receiving both GPS and a significant visual update, an analyst calls WWDC's opening "D-Day" for new iPhone models, and the latest SDK for the handset may allow background apps.

iMac refresh entering retail tracking systems

Following a recent Geeksugar report, details of Apple's first update to the aluminum iMac have filtered into retail, AppleInsider has heard.

A memo distributed among some of Apple's stateside channel partners this week has reportedly provided a heads-up on the refresh, informing them that the changes will primarily touch on the systems' processors and hard drives rather than a significant redesign.

People familiar with the matter tell AppleInsider that placeholders for the new desktops have already been entered into Best Buy's inventory system. How many models will be available is unknown, although a second report indicated seven part numbers entering the system, three of which were dedicated to memory upgrade kits.

Not all resellers are being made aware of the update, however. Checks with multiple American suppliers show them to have ample stock of all existing iMacs save for the Core 2 Extreme version, while the only clue from other regions is a mention from Ingram Micro's European division, which was told without warning that it could order current iMacs with a greater than normal discount.

Apple never slashes prices for resellers without specific reasons, European sources note.

New 3G iPhone rumor claims GPS, flush audio jack

Escalating the already rampant speculation about an iPhone with third-generation cellular Internet access, Engadget on Friday claimed to have new information regarding the Apple device from a "trusted source" who has used the future handheld.

The new iPhone will have the expected 3G access, but should also have a "proper" GPS receiver that lets it track map data in real time, the alleged tipster says. Apple will also have addressed complaints of the recessed headphone jack limiting choices and is now believed to have placed the jack flush with the outside, allowing any standard earphone set to work properly.

Cosmetically, the phone is said to resemble a purportedly leaked image released by iPod Observer that shows the anodized aluminum back replaced with a glossy black case. The volume switch is also now chrome.

Apple's refresh is "slightly" thicker and more rounded than the 0.44-inch thick model sold today, the report adds, but will otherwise be fairly similar.

The rumor goes against prevailing expectations, however, by suggesting that Apple may not ship or even announce the 3G update until July. This clashes with analyst predictions of the phone's debut at WWDC in June, many of which have been triggered by promotional discounts for the iPhone in Europe.

However, the mention of mapping technology supports claims that Apple's iPhone SDK has contained GPS references inside its emulation code that would only be applicable to actual hardware, and not simply Apple's data-based triangulation method used today.

Analyst: WWDC is 3G iPhone's "D-Day"

Likening Apple's phone efforts to a famous World War II beach invasion, Citi analyst Richard Gardner this week called Apple's Worldwide Developer conference the "D-Day" for a 3G iPhone that would also begin an "impressive wave" of new products.

This would include not just the next-generation firmware and software development kit but also a hectic update schedule over the three months following the developer event.

"We expect a complete refresh of the laptop and iPod lines," Gardner says. "The SDK should [also] yield hundreds of compelling iPhone/iPod touch third-party apps for by [sic] Christmas."

Citi's researcher also predicts good fortune for Apple through a "tailwind" of cheap memory and other components, though cautions that gross margins may be smaller in the near term as Apple may have bought some memory prematurely at the end of last year, missing out on an important price cut.

iPhone SDK beta may contain hooks for background apps

Further exploration of Apple's newest iPhone SDK beta appears to contain program calls that could be used for running third-party applications in teh background, TUAW reports.

Methods are included in the UIApplication delegate class that refer to both enabling and giving up status as the active application -- a technique used in many programs to keep them running but change certain behaviors when the app gains primary focus.

Apple's guidelines for iPhone development have so far barred background use for all but its own software, effectively ruling out instant messaging clients and other software that depends on constant activity.

Such rules aren't known to have changed with the latest SDK release but would conflict with these code changes.