Nearly three months since the manic debut of the iPhone 5s, Apple’s high-end smartphone for 2013 is now shipping "within 24 hours." Courtesy / Dave Smith

The iPhone 5s was “grotesquely unavailable” shortly after its initial release date of Sept. 20 -- a consequence of both high sales (Apple broke its iPhone sales records with 9 million iPhone units sold in the first three days) and severe supply constraints, especially for the highly sought-after silver and gold models. But nearly three months since the debut of the iPhone 5s, availability for Apple’s high-end smartphone for 2013 is much improved, as the iPhone 5s is now shipping “within 24 hours.”

Initially, Apple had trouble keeping up with demand, as shipping times for the iPhone 5s quickly slipped to 10 days shortly after midnight on Sept. 20, and later that day, shipping estimates slipped further to between two and three weeks and sometimes even longer.

In November, Apple’s largest manufacturing partner, Foxconn, reportedly shifted its focus from the less popular iPhone 5c to the hotter iPhone 5s; other Apple suppliers also ramped up their production of the iPhone 5s to accommodate demand for the higher-end model, which has been reportedly outselling the iPhone 5c by more than a 2-to-1 margin, according to Consumer Intelligence Research Partners.

Since the start of December, availability of the iPhone 5s has improved drastically, nearing the point of 100 percent availability for all colors and storage capacities via Apple’s online store as well as its physical retail stores. But for holiday shoppers looking to purchase a new iPhone 5s as a Christmas gift, Apple still recommends consumers check the company’s shipping guidelines to ensure the iPhone 5s arrives by Dec. 24. According to Apple’s guidelines, consumers should order the iPhone 5s by midnight on Dec. 18 to receive the phone by Christmas Eve.

If you want an iPhone 5s anytime soon, you might want to act fast. Apple and China Mobile are putting the finishing touches on their agreement to release the iPhone 5s and iPhone 5c on China Mobile's expansive TD-LTE network, which boasts about 740 million customers -- that's more than all of the customers from Verizon Wireless, AT&T and Sprint combined. China Mobile will reportedly open pre-orders for the iPhone 5s and iPhone 5c on Thursday, which may affect the availability of iPhone supplies in other countries (including the U.S.) as we approach the all-important gift-giving season.

About The iPhone 5s

The new iPhone 5s is an impressive improvement over the iPhone 5, even though both phones have the same form factor. The iPhone 5s features the same 4-inch Retina display and chamfered diamond-cut edges, but the phone also comes with a number of new innards. The iPhone 5s is powered by a new A7 processor -- with CPU performance 40 times faster and GPU performance 56 times faster than the original iPhone -- and Open GL, just like the new Nexus 7. To supplement the A7 chip, the release of the iPhone 5s also comes with Apple's new M7 chip, which contains all the motion-tracking hardware Apple needs to make its iWatch a reality. By packing so many components into the M7 motion co-processor, including an accelerometer, gyroscope and compass, the M7 can continuously measure motion data for the newest generation of health and fitness apps.

The iPhone 5s also features a slightly modified battery for greater life, a new and improved camera system packed with new features and technologies that make for better quality images and videos, and a fingerprint sensor called Touch ID, which lets users authenticate ownership and user passwords by simply holding their thumbs on the iPhone’s signature home button. Apple chose to release the iPhone 5s in three color options -- white with silver, white with gold and black with space gray -- but for more information on the new iPhone 5s, check out our review and hands-on with the seventh-generation iPhone, and learn more about why it's worth the price to upgrade.

What do you think of the iPhone 5s? Would you purchase the iPhone 5s over the iPhone 5c, despite the $100 price difference? Are you impressed by the features in the iPhone 5s, or do you prefer another smartphone out there? Let us know your thoughts in the comments section below.

Follow Dave Smith on Twitter