San Francisco - The so-called Google-phone went on sale for the first time in cities across the US Wednesday, offering the strongest competition yet to the dominance of Apple's iPhone.

German-owned carrier T-Mobile began offering the G1, made by Taiwan's High-Tech Computer (HTC), in cities where T-Mobile's 3G service is available, including Boston, Chicago, Dallas, Los Angeles, Minneapolis, New York, and Seattle. The company made its first retail sale of the G1 Tuesday evening in San Francisco.

Along with 3G support, the G1 features a touch screen, a full QWERTY keyboard, and GPS, Wi-Fi, and Bluetooth connectivity.

The phone is powered by Google's open-source Android software, which is optimized for the use of Google services over the mobile internet, which Google sees as an ever more important medium for advertising dollars.

Google has already released the Android code to open source developers and other manufacturers are expected to roll out more phones based on the software in the coming months.

To help develop Android, Google also formed the Open Handset Alliance - a partnership of more than 30 firms that includes operators such as Telefonica, handset makers such as HTC and Motorola as well as chip makers such as Intel and Qualcomm.

Initial reviews of the phone have been positive, with most evaluations regarding it as a worthy competitor to the iPhone, even if it does lack some of Apple's signature style.

In addition, it offers features that the iPhone lacks, such as a keyboard, removable battery, SD card slot, a better camera and the ability to run several programs at once. It also makes using Google products such as Gmail, Maps and Calendar easy to use.

However, it is not optimized for listening to music since it has limited storage and needs an adapter to use with regular headphones.

The G1 costs 180 dollars with a two-year service agreement and mail-in rebate. The phone without a service plan costs 400 dollars. The G1 will be available in the UK in November and across Europe in the first quarter of 2009. (dpa)