Apple will today ship the latest version of its operating system for the iPhone and iPod touch, iOS 4. We are also hearing that Apple has begun shipping the iPhone 4 to customers who pre-ordered the device.

The company may already be shipping devices with the new OS installed, according to one report.

We are hearing divergent reports as to when the OS will actually ship.

Most industry watchers expect the new OS to ship at or near 10am Pacific Time.

Some users already have iOS 4 installed on their devices, thanks to curious iPhone developers who noticed the beta made available to them could easily be installed on an iPhone.

iOS 4 offers over 100 new features, including Multitasking, Folders, enhanced Mail, deeper Enterprise support and Apple’s new iAd mobile advertising platform (which launches July 1).

We’ll also see the iBookstore fully embrace the iPhone, which is nice.

Not all features function on every iPhone model.