Apple Inc.'s iPhone5 remains the most anticipated smartphone in the U.S. market, and appears to have broken all kinds of records when it comes to rumors surrounding a device.

Since January, bits and pieces about the next-generation smartphone have been making the rounds on the Internet, with different rumored specifications and concept images offered by various Web sites and blogs.

Apple is a couple of days away from announcing the arrival of the most anticipated iPhone to enter the U.S. smartphone market. The company has issued invites for an event Tuesday that will showcase the fifth-generation iPhone.

The iPhone5 is expected to run on the latest iOS5, which will come with 200 new features, including an improved notifications system, as well as the Newsstand and iMessage applications. In addition, the iPhone5 is expected to feature the new iCloud service for operating iTunes, enabling wireless remote access of purchased and personally collected music from all computers and mobile devices.

The iPhone5 will likely support HSPA+ networks that will provide faster Internet speeds compared with its predecessors, Japanese blog Macotakara reported, citing a China Unicom executive's presentation at Macworld Asia.

The arrival of the iPhone5 will trigger a smartphone battle in the U.S. market as its strongest rivals -- the Samsung GalaxyS2 and Motorola Droid Bionic -- have come to this market after several design changes.

Samsung's GalaxyS2 continues its strong march in the smartphone race, giving stiff competition to Apple's iPhone4 as well as the upcoming iPhone5.

The GalaxyS2, which runs on the Android 2.3 Gingerbread OS and sports Samsung's TouchWiz UI, comes with an 8-megapixel camera with flash and can record high-definition video in 1080p, offering the richest video content on a smartphone. The phone also has a front-facing 2-megapixel camera for video chat.

The device, which was recently launched in the United States, sold a whopping 10 million units since its launch in late April 2011, not including sales from the U.S., the largest market for smartphones.

On the other hand, Apple sold 20 million iPhones in the third quarter. Though the Galaxy S2's sales lag behind iPhone sales, it implies that the Samsung Galaxy S2 is the toughest rival Apple will face for its iPhone 5, which is expected to be launched in October.

Meanwhile, the Motorola Droid Bionic has undergone several design changes. At the beginning of this year, this smartphone looked like the Motorola Atrix, but now it looks very similar to the Motorola Droid 3, one of the latest high-end phones. However, the Motorola Droid 3 has a slider QWERTY, unlike the Droid Bionic, which is just a touchscreen phone.

Other changes in the Droid Bionic include higher RAM capacity, a change in chipset from the Tegra 2 AP20H to the TI OMAP4430 and, surprisingly, less battery capacity compared with the battery capacity introduced in previous iterations of the phone.

So the heated battle will begin with the arrival of the Apple iPhone 5. All the three smartphones are right up there in the hype cloud, and hopefully they will live up to it.

Meanwhile, Samsung has announced a press event on Oct. 11, exactly one week after Apple's Let's talk iPhone program on Oct. 4. It is expected that Nexus Prime, the flagship smartphone for the Google Android platform, will be officially presented at the Samsung event.

Samsung's Nexus Prime will be the first smartphone with an Android 4.0 operating system, codenamed Ice Cream Sandwich, which is designed to provide strong competition to Apple's iPhone 5.