T-Mobile showed off its new G1 mobile phone at a press event in New York Tuesday, thus becoming the first carrier to offer a device run on Google’s Android open source mobile platform.

The device, which was developed by device manufacturer HTC, has many of the features commonly seen on many of smartphones on the market, including a touchscreen with drop-and-drag capabilities, a pull-out QWERTY keyboard, and a host of Web-based applications for maps, music and instant messaging. 

But the big reason that the phone has generated buzz in recent weeks is because it will be the first ever to run on Android, a Linux-based open source mobile platform that Google first debuted last November. Google has long said that the goal of the platform would be to spur innovation within the mobile development community and also to give users the ability to switch to new carriers without switching their mobile devices. What a Google-based phone would look like has long been the subject of speculation.

Interestingly, the G1 will not let users connect to other Android-supporting networks, as anyone who purchases the device will have to sign a two-year voice and data agreement as a precondition. Andy Rubin, Google’s senior director for mobile platforms, said that the T-Mobile G1 was still an important development because it would open mobile networks to support new and innovative applications created by third-party developers.

“Developers will obviously be able to use this as a platform to develop new applications,” he said. “But also, because of its openness, developers will be able to modify the platform and make the platform better.”

Google and T-Mobile invited along some third-party application developers to give demonstrations of their Android applications, including the Ecorio application that uses Android's GPS capabilities to track a user's carbon footprint while driving in a car, and the ShopSavvy application that lets users compare prices for products sold in nearby stores by scanning their barcodes with the G1’s built-in camera. To encourage application development, Google announced last year that it would give $10 million worth in prizes to software development companies to develop innovative and useful applications for the platform, and Google recently announced the winners.

Cole Brodman, the chief technology and innovation officer for T-Mobile USA, said that T-Mobile is hoping to give its  customers a mobile Internet experience comparable to the Web experience they get on their home computers. The phone will run best on local Wi-Fi networks or on T-Mobile’s GSM-based Universal Mobile Telecommunications System (UMTS) 3G network. T-Mobile officially launched its first US-based 3G network in the New York this past spring, and the carrier has live 3G coverage in 16 major markets, Brodman said. The company  plans to have 3G coverage in 22 major markets by mid-November, Brodman added.

Web browsing on the phone will be done using a mobile variation of Google’s Chrome operating system that Rubin said would be based on the WebKit open source browser engine.

T-Mobile’s unveiling of the world’s first Android phone comes ten months after Google first announced its intention to distribute Android as an open source mobile operating system. U.S. carriers Sprint and Verizon have also committed to eventually supporting Android-based devices on their networks.