On October 22, T-Mobile will reap the benefits of its founding membership in the Open Handset Alliance. Through an exclusive partnership with Google and Asian handset manufacturer HTC, the T-Mobile G1 will become the first shipping mobile device based on the Android platform.

Google and company have worked hard to make the T-Mobile G1 both affordable and easy to use. And while it's too soon to know how far developers will take the open source Android platform, we now know what to expect from the first Android phone to arrive on store shelves.

The T-Mobile G1's hardware design will be familiar to users of HTC's Windows Mobile handsets, a lineup that includes the AT&T/Cingular 8525 and T-Mobile's own Wing, both of which I reviewed for InfoWorld and continue to use. This mature design, with fashionably subtle tactile buttons underneath the display, incorporates a touch screen that's sensitive to both fingertip and stylus, as well as a slide out full QWERTY keyboard. (In T-Mobile G1's case, the keyboard swivels out in a half-moon motion while remaining parallel to the display.) That's right, it's got actual keys that don't take up any space on the screen, and the keyboard disappears when you don't need it. When you flip out the keyboard, the display rotates from portrait to landscape view -- again, mimicking the behavior of HTC's Windows Mobile line.

As implemented on the T-Mobile G1, the Android user interface incorporates an iPhone-like flick gesture to scroll and to flip among multiple pages in a document. HTC debuted this feature as TouchFlo in some of its latest Windows Mobile handsets, and it will be built into its upcoming Touch Diamond and Touch Pro handsets as well. HTC's implementation of the slide-out keyboard works extremely well. Android's context menus, activated by a touch-and-hold gesture, are presented as large buttons that fill the width of the display. The menus provide cut and paste of multiple object types (text, graphics, HTML) across applications. The Android platform is fully multitasking, supporting multiple simultaneous foreground applications as well as software services that run in the background (daemons) without user interfaces. The flick gesture also sweeps through pages in a document, supplants tabs in the browser, and pages through icons on the home screen. An application window can be pushed off or pulled onto the display like a window shade, making multiple running apps easy to access. Incidentally, the design of the browser seems more derived from Nokia's S60 WebKit-based browser than from Google's Chrome.

Context menus, cut and paste, and multitasking are among UI features that set a sharp contrast with T-Mobile G1's clearest competitor, iPhone. And, of course, Android's UI is fully customizable, from skinning and themes to completely trashing it and replacing it with something else. The full-on gearhead will distinguish himself or herself by brandishing a text console as the primary UI. I'd bet a week's pay that work on a convincing iPhone skin is already underway.

The very Google applications that help define iPhone, namely Google Maps and the YouTube viewer, are present on the T-Mobile G1 as well, but with a bit of a kick. T-Mobile demonstrated street-level maps that include photographs of landmarks that match the user's perspective. Using the device's GPS and accelerometer, the T-Mobile G1 becomes a sort of viewfinder: As you turn yourself around and tilt the device, the display shows what Google Maps thinks the scene in front of you should look like. This it deduces from where it thinks you are or plan to go, the direction it thinks you're facing, and the photograph that it thinks is most recent and relevant.