Andy Rubin, one of the co-founders of Android who went on to become SVP of mobile and digital content at Google, wasn't new to the mobile device game. His earlier venture, Danger Inc., had found success in 2002 with its Hiptop smartphone, which was rebranded by T-Mobile as the Sidekick. It's not surprising then that the G1 ended up as a T-Mobile exclusive -- after all, its pop-out keyboard was reminiscent of the Sidekick's swivel screen design. And for consumers in search of an alternative to the BlackBerry smartphones that dominated at the time, the G1 was a welcome option.

The T-Mobile G1 was an odd-looking duck. It was chunky due to the phone's pop-out keyboard, with slightly larger dimensions than the sleek iPhone 3G released the same year. The G1's physical keyboard was a necessary evil considering the inaugural Android operating system (1.0) didn't include a virtual one -- this despite its 3.2-inch capacitive touchscreen. That wasn't the G1's only design quirk: It also featured a slanted "lip" on its front face that housed a trackball and physical navigation buttons.

Its unique build aside, the G1's main attraction was its open-source Android environment. With it, Google aimed to stimulate app development and "future proof" the OS with developer contributions over time. The Android Market (now known as Google Play) also debuted in tandem with the G1, offering around 50 applications at the time. All those apps were free, too, since the Market had yet to implement a payment system.

Multitasking, copy and paste, pull-down notifications and home screen widgets: These were some of the fresh features the G1 ushered in. It also, unsurprisingly, came deeply integrated with Google services such as Gmail and Maps. And without a proprietary music application of its own at the time, Google turned to Amazon to provide an MP3 app.

The G1 may have been an unfinished product when it was released, but Google addressed its shortcomings with iterative software updates -- now a common and accepted practice for Android devices. Early OS fixes tackled glaring oversights like the G1's missing virtual keyboard and lack of video-recording ability for its 3-megapixel rear camera.

A T-Mobile rep compares Apple's iPhone 3G (at left) with the G1.

A year after the G1's launch, Verizon released the massively popular Motorola Droid with a slightly tweaked version of Android; a device that would prove a boon for Android device sales and mindshare. Still, Google continued on its own parallel path with HTC, releasing the MyTouch series and the G2. Eventually, however, Google abandoned its partnership with T-Mobile and HTC in favor of its Nexus line: reference devices that would run the latest, unadulterated versions of the Android operating system.

Google's G1 smartphone holds an important place in the company's history. Not only was it the first of many devices to run the Android OS, but it also stood out as an open-source alternative to Apple's iPhone and closed iOS ecosystem. Android's openness and flexibility led to its rapid adoption by a variety of manufacturers seeking to topple Apple's success -- it also helped that it was free to license. The G1, though primitive in comparison to the current crop of Android devices, was Google's first step toward the mobile phone market domination it enjoys today.

Did you own a T-Mobile G1? Add it to your Engadget profile as a device you had (or still have) and join the discussion to reminisce or share photos of your device with other like-minded gadget fans.

[Image credit: T-Mobile / HTC (G1 front view); JENS SCHLUETER/AFP/Getty Images (iPhone/G1)]