Google's rival to the iPhone and Blackberry phones goes on sale in the UK today.
The G1 - the subject of the latest high-profile launch last month - is designed around improving the speed and quality of using the internet on mobile handsets.
It will go head to head with Apple's iPhone, the Blackberry and other smartphones from makers including Nokia when it is released exclusively by T-Mobile today.
It will be available for free on price plans from £40 a month.
The gadget uses Google's Android software and is being touted as a phone with the capability of a hand-held computer.
It provides access to Android Market, which lets third party companies offer applications to users.
Other manufacturers are expected to produce their own Google phones over the next 12 months.
The phone makes use of Google Maps, instant messaging through Google Talk as well as high-speed internet browsing and a 3-megapixel camera.
Analysts have said the gadget could potentially transform the mobile telephone market by providing service supported by advertising instead of subscription fees.
But some believe the phone may struggle to compete with the iPhone.
Ernest Doku, from mobile phone comparison website Omio.com, said: "Despite the popularity of the Google brand, the G1's design lacks the inherent 'cool' factor that made the iPhone 3G such a mass market success for Apple.
"The launch of the G1 is important not only because it's Google's first foray into the mobile market but because it's also the launch of an entirely new mobile phone operating system.
"Android is the equivalent of releasing an alternative to Microsoft's Windows - and equally as risky."
T-Mobile UK managing director Jim Hyde said: "It's set to revolutionise the way we use the internet on our mobiles.
"It's uniquely built for effortless online communication whether you want to email, text or blog, and with access to some groundbreaking applications on Android Market, the possibilities really are endless."