Thanks to a new iPhone OS 4.0, the fourth-gen iPhone might multitask, run cutting-edge maps, and overlay useful information about nearby buildings on top of live video. You might be able to interact with it using a bunch of new multitouch gestures, stream your media off the cloud, and more.

New pieces of information regarding the iPhone OS 4.0 that are arriving on a daily basis in the run-up to Apple’s January 27 event help paint a better picture of the fourth-generation iPhone, simply regarded to as 4G iPhone. We’ve written quite a lot thus far about its rumored hardware features, ranging from new sensors like RDIF to front-facing camera for videoconferencing to speedy custom chips.

Beyond the hardware, though, the biggest surprises are said to be in the new underlying software and online services. An updated iPhone OS 4.0 software is the cornerstone of the next iPhone and its powerful hardware even though the software should run on the existing iPhone 3G and 3GS devices as well. A tipster in the know told Boy Genius Report that the iPhone OS 4.0 will

put Apple ahead in the smartphone market because it will make them more like full-fledged computers more than any other phone to date.

The same source said that multitouch gestures will be system-wide and used much more extensively than in the current 3.x version that only employs pinch zoom and swipe gestures in the Safari and Photos apps. Apple has also found “a few new ways,” a source said, to multitask apps. iPhone OS 3.x allows only one running app at a time and doesn’t allow third-party apps to multitask arguing that background processes drain the battery. Finally, a source made mention of “brand new syncing ability for the contacts and calendar apps” (perhaps syncing with third-party services like Google, not just with Apple’s $99 a year MobileMe) and UI changes that should simplify navigation.

On the service level, though, Apple is said to be breaking away from its dependency on Google by developing their own replacement services. More precisely, 4G iPhone could run cutting-edge maps called iGuide featuring more detailed overlays and live information, courtesy of Apple’s quiet acquisition of a mapping startup Placebase last July.

Various augmented-reality features also come in mind, such as the ability to detect nearby buildings and other points of interest on images and videos. Finally, as Geek reported earlier today, cloud iTunes might also allow 4G iPhone to stream your entire personal music and video library on demand, off the cloud.

iPhone OS 4.0 is expected to power not only a future iPhone model, but a rumored tablet as well. Apple invited the press to its January 27 media event at the Yerba Buena Center for the Arts in San Francisco to “see its latest creation.” Big media agrees that Apple will unveil iPhone OS 4.0, 4G iPhone, and a tablet at the event. Other items on the agenda could include multitouch iLife and iWork suites, Core i5 MacBooks, and more.

Meanwhile, a French-language site Nowhereelse.fr has published (original in French, Google translation) an interesting mockup visualizing 4G iPhone rumors. Based on a cool rendition by an agency called Designed By Item that depicts a unibody-created 4G iPhone, the mockup lists key rumored featured with an estimated probability of ending up in the actual product:

• Glowing Apple logo on the back: 1 percent
• removable battery: 30 percent
• Built-in RFID: 30 percent
• Portable DVR functionality: 30 percent
• full metal case (unibody): 40 percent
• LED flash: 50 percent
• 64GB NAND flash memory model: 60 percent
• front-facing video camera: 70 percent
• contacts on home screen: 70 percent
• touch-sensitive case: 75 percent
• Dual-core processor and more RAM: 80 percent
• OLED display: 90 percent
• Five-megapixel camera: 90 percent
• Availability between May and July: 99 percent

Check out the below composition (click for the full-size version) and let us know what you think about the next iPhone and its rumored features in the comment section.