Apple Inc.'s iPhone 4S, which was unveiled Oct. 4, has already become a huge success among customers, even before it went on sale in stores across the globe Friday.

Carriers Verizon, AT&T and Sprint have said pre-orders have already been sold out, while Apple said earlier that it logged 1 million orders 24 hours after it opened pre-orders for iPhone 4S, an all-time record for the company. According to analyst estimates, iPhone 4S sold 3 million units in the first weekend.

iPhone 4S is not the iPhone 5 that was forecast by the rumor mills, but that still doesn't make it a lesser device. The phone has significant hardware upgrades, though it looks identical to the iPhone 4.

It does feature some important specs attributed to the phantom iPhone 5, like 1 GHz dual-core ARM Cortex-A9 processor, PowerVR SGX543MP2 GPU, an Apple A5 chipset and an 8-megapixel camera. It also has features like a 3.5-inch TFT Retina multi-touch display and is loaded with the latest Apple operating system iOS 5.

iPhone 4S also comes with alternating antennae for better call reception, CDMA and GSM support, a personal assistant called Siri, iCloud and Bluetooth 4.0 wireless technology. However, missing were prominent specs like edge-to-edge design, a larger display, 4G LTE and Near Field Communication technology.

One big rival of the iPhone 4S will be the Motorola Droid Bionic. The much anticipated Motorola Droid Bionic hit the shelves in September, more than eight months after the device was unveiled at the Consumer Electronics Show in Las Vegas, Nev. in January. The phone is completely modified from the original one introduced during CES 2011.

Specs on the Droid Bionic are impressive; Droid comes with a lot of the standard qualities which have made Droid a household name in smartphones. This includes a 4.3-inch HD screen with a Corning Gorilla scratch-free screen, two cameras: front-facing for video chat and 8-megapixel back camera, Adobe Flash preloaded, 32 GB of memory and a slim frame.

The smartphone also comes with Video Surf, a Shazam-like app for videos, Motoprint for wireless printing, NFL Mobile and support for Netflix.

It will be interesting to compare the features of the two competitors.

Size: Droid Bionic has a dimension of 127.5 x 66.9 x 10.99 mm and weighs up to 158g (5.6 oz). On the other hand, Apple iPhone 4S comes with 115.2 x 58.6 x 9.3 mm and weighs 140 grams.

Display: The iPhone 4S will have a 3.5-inch TFT Retina multi-touch display, with 960x640 resolutions at 330 ppi pixel density. The Motorola Droid Bionic has a 4.3-inch qHD screen that should give a resolution of 960x540-pixel at 256 ppi pixel density.

Camera: The Motorola Droid Bionic has an 8-megapixel auto-focus camera with 3264×2448 pixels, autofocus and dual LED flash, as well as a front-facing camera for video chats. The camera can shoot HD videos of up to 1080p. The iPhone 4S also comes with an 8-megapixel, 3264×2448 pixels, autofocus, LED flash camera in the front. It features a VGA front-facing camera. The camera can also shoot HD videos of up to 1080p.

Operating System: Motorola Droid Bionic runs on the Android 2.3.4 Gingerbread OS, while the iPhone 4S is loaded with the latest Apple operating system iOS 5, which brings more than 200 new features to the iPhone.

Processor: Motorola Droid Bionic comes with a dual-core 1GHz ARM Cortex-A9 processor, ULP GeForce GPU and Tegra 2 AP20H chipset, while the iPhone 4S features 1 GHz dual-core ARM Cortex-A9 processor, PowerVR SGX543MP2 GPU and an Apple A5 chipset.

Storage: The Motorola Droid Bionic has 16GB internal storage and another 16GB microSD card preinstalled, which can be expanded to 32 GB. The iPhone 4S comes in 16GB, 32GB and 64GB models. It doesn't support a MicroSD card slot.

3G/4G: Droid Bionic has Rev. A up to 3.1 Mbps. Apple iPhone 4S, on the other hand, has HSDPA 14.4 Mbps and HSUPA 5.8 Mbps support. iPhone 4S also has CDMA EV-DO Rev. A (800, 1900 MHz) technology.

Battery: The Motorola Droid Bionic has a standard 1735 mAh battery offering talk time of 650 minutes and standby time of 200 hours, while the iPhone 4S has a Li-Po 1,420 mAh battery, with 8 hours of talk time on 3G and up to 14 hours on 2G networks (GSM).

Price: The iPhone 4S costs $199 for the 16GB model, $299 for the 32GB model and $399 for the 64GB model. The Motorola Droid Bionic is priced at $299 with a two-year contract from Verizon.

Must Read : iPhone 4S Launches Today: Top 10 Reasons Why Apple's New iPhone is Worth Buying (PHOTOS)
Must Read : iPhone 4S With iOS 5 and Siri Begins Shipping Today: Should Rivals be Afraid?
Must Read : iPhone 4S Hits Stores Today: How and Where to Buy Apple's Latest Smartphone Without Pre-order

READ MORE: iPhone 4S Goes on Sale Today: How, When, Where and Why You Should Buy Apple's Best Ever Smartphone (PHOTOS)