Apple this weekend began preparing its retail segment for the imminent launch of the company's much-anticipated white iPhone 4 models, signaling the end of a somewhat embarrassing delay that has seen the handsets elude eager buyers since last July.

According to people familiar with the matter, Apple's U.S-based retail stores began receiving promotional information overnight that features the white iPhone 4, expected to launch for both Verizon and AT&T subscribers "within the next week."

In addition, several stores are said to have received shipment notifications for the various white iPhone 4 SKUs and have been instructed to hold those shipments in the back of the house until further notice. All indications point to an official announcement by Wednesday, April 27th.

Word that white iPhones are finally en route to Apple stores in the U.S. comes just days after the inventory systems of U.K.-based wireless carrier Vodafone indicated stock of the handsets while photos of a 16GB model in official retail packaging -- carrying model number MC604B/A -- were published online.

The arrival of white models is expected to serve as a boon for iPhone sales during a time of year when customers have historically held off purchasing new iPhones under the expectation of next-generation models making their debut during the summer.

This year, however, Apple is widely reported to have decided to forgo a summer iPhone introduction in favor of introducing so-called fifth-generation models in the fall, much closer to the holiday shopping season. According to AppleInsider's sources, these new models will go into production in September and sport a unified Qualcomm baseband capable of serving both GSM and CDMA networks.

Such a move is also expected to allow the Cupertino-based company to align fifth-generation iPhones for a simultaneous release on both GSM and CDMA networks, meaning both AT&T and Verizon customers should be able to buy the new handsets later this year at the same time.

Apple has publicly pushed back the release of the white iPhone 4 several times over the past 9 months. In late July of last year, the company revealed that it would not be able to launch the handset alongside black models that month as it had originally planned. Instead, Apple rescheduled the launch for "Late 2010" only to concede a few months later that it would miss that self-imposed deadline as well, telling customers not to expect white models until the Spring of 2011.

This March, however, AppleInsider exclusively reported that Apple had finally begun production of the white models, which would become available to customers by April. The company was said to have made changes to both the handset's original "film material" and paint mixture that were resulting in the production of a "huge" number of defective units.