**Editor's Note: Click here for our list of August's hottest selling smartphones to see how the iPhone fared against the competition, or here for our top 10 list of best smartphones in 2013 (so far).**
Pre-orders for Apple's iPhone 5c have already began in some areas, with the so-called "budget" device slated to go on sale on Sept. 20. Meanwhile, the flagship iPhone 5s is not available for pre-order and has sparked fears that there will be a shortage when it is released on Friday.
The new fingerprint scanner – making its debut on the 5s – could be a reason for concerns about delays. According to Peter Misek, an analyst at Jefferies & Co., Apple's manufacturers in Asia won't be able to produce them quickly because the scanner is complex, according to SidhTech.
Only 5 to 10 million 5s handsets are expected to be produced this quarter, while 30 million iPhone 5Cs and 5 to 8 million iPhone 4S handsets are expected to be produced, Misek said. He predicts that 20 to 25 million 4S handsets and around 30 million 5c handsets will be built in the last quarter of the year.
The iPhone is always popular at launch. Only time will determine how fast the 5s supplies drain before the next shipments come in.
All major U.S. carriers – AT&T, Verizon, Sprint and T-Mobile – now offer the iPhone. So do a handful of regional and prepaid carriers.