Apple opened the pre-order for its latest iPhone 5 early on Friday, Sept. 14, morning and the Cupertino tech giant sold out the initial lot of iPhone 5 in just one hour.

The shipping times have been pushed back from the expected launch day on Sept. 21. Users who have pre-ordered through the U.S. online Apple Store should expect the scheduled shipment in two weeks.

Many iFans persevering to pre-order the iPhone 5 on Apple's Web site were left disappointed as visitors to the site were greeted with a "We'll be back" notice.

"Customers may still be able to receive launch-day delivery by ordering through their carriers. AT&T, Verizon, and Sprint are listing 9/21 delivery dates at the time of this posting -- but those dates may not immediately reflect available stock," reports MacRumors.

Furthermore, MacRumors indicates that iFans may also purchase the iPhone 5 on Sept. 21 by visiting an Apple retail location. "Apple is opening retail stores at 8 a.m. that day for the launch."

Alongside the carriers and Apple, Walmart is also accepting pre-orders for the iPhone 5. Walmart is offering the 16GB version of the iPhone 5 for $189.97 instead of the usual $199 price tag.

Last year, post the iPhone 4S launch, AT&T revealed that it received 200,000 pre-orders of iPhone 4S within the first 12 hours of sales. This year, carriers may find an increase in the number of pre-orders. Estimates that Apple's iPhone 5 sales may climb as high as 10 million units in the first week itself, may come true fruition if this trend continues.

iPhone devotees, who want to grab the smartphone on Sept. 21 itself, will have to take a chance and physically visit the Apple store. However, iFans should not be surprised if they find a huge queue at the Apple store, prior to the opening time.

Update (Sept. 15, Saturday, 1.50PM EDT) : Good news, iFans! The "We'll be back" notice has been lifted. But we'd advise you to pre-order your device before stock runs out.