As promised, Google has unleashed a new web-based Gmail incarnation that runs on both the Apple iPhone and Google's very own Android mobile platform.

Last week, at Tim 2.0'Reilly's Web 2.0 Expo, Google vice president of engineering Vic Gundotra showed off a "technical preview" of the new HTML 5 Gmail, hinting that a release was just around the corner. And this morning, the company followed through, announcing the new client web service with a post to the official Google Mobile blog.

By way of Google Gears and HTML 5 - the next-generation web lingua franca still awaiting approval from World Wide Web Consortium (W3C) - the new email service benefits from so-called "app caching," letting you access recently received messages even when you're offline.

"If the data network drops out on you, rest assured that Gmail won't," reads today's blog post. "You'll still be able to open recently read messages and to compose over a flaky, or non-existent, network connection."

Google has also added what it insists on calling a "floaty bar," designed to help with message sorting and navigation. As you move through your messages, this compact menu moves with you, letting you, say, archive or delete messages without scrolling back to the top of your inbox. Scrolling back to the top is required if you want the search box, but that's better than scrolling to the bottom, where the box used to be.

And naturally, Google says the new service is faster - and better looking. "Labels are easier to read and are more in-line with the familiar Gmail labels you see on your desktop."

That's it. But Google boasts that the switch to HTML 5 and Google Gears will speed up future tweaks. "The full impact of this new architecture isn't visible yet, but it will enable us to significantly improve performance and quickly roll out new features in the near future," Google mobile engineer Joanne McKinley writes.

The new Gmail for mobile runs on any Android phone, but if you're an iPhone or iPod Touch user, you'll need the Apple's 2.2.1 firmware or later. Otherwise, you'll be redirected to the existing version of Gmail for mobile ®

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