Apple will begin taking pre-orders for the iPhone 5c on Sept. 13, but will not be doing the same for the iPhone 5s, indicating that the 5s will be in short supply.

If you plan on purchasing an iPhone 5s on its September 20 launch date, you might want to prepare to wait in long lines at Apple retail stores or carrier shops prior to its official release. Apple has not explained why it's taking pre-orders for the iPhone 5c and not the iPhone 5s, something it has done with each previous flagship smartphone.

It appears that one likely reason for this decision stems from a report that came out in July. Supply constraints of the iPhone 5s' new Touch ID fingerprint scanner were reportedly going to cause a delay in commercial production of the new iPhone.

"Poor yields of fingerprint-recognition chips and LCD driver ICs will likely force Apple to reduce first-quarter shipments of the rumored iPhone 5S, which is slated for launch in September 2013, according to industry sources. Volume production of fingerprint-recognition and LCD driver chips for the iPhone 5S should have started at the end of June or early in July, but issues related to yield rates will delay commercial production of the two chips to the end of July, therefore affecting the initial supply of the iPhone 5S," reported DigiTimes at the time.

In recent years Apple has always offered pre-orders of its latest flagship iPhone, either by allowing customers to have the handset shipped to their home on launch day or reserve the device to pick up in an Apple retail store. This made it very convenient to ensure that you received the latest and greatest iPhone on its first day of being available, without having to deal with the typical long lines at Apple stores or carrier shops.

While some might think this is Apple's way of drumming up interest in the iPhone 5s and getting major news coverage with long lines, the company would likely much rather prefer to sell as many pre-orders as possible of both iPhone 5s and iPhone 5c before its official release.

If you want an iPhone 5s on September 20, prepare to wait in long lines ir order to get your hands on one.