Google announced at its I/O Developer Conference today that it will release Ice Cream Sandwich, the next release of its phone operating system, later this year.

In many ways, it will be the company’s most ambitious release. Hugo Barra, director of Android product management, told the large crowd at the keynote (and thousands watching via live streaming video) that the top priority is to make the platform easier for developers. Application frameworks will also be a big focus in order to eliminate fragmentation across form factors.

In the meantime, Android 3.1—an update to the Honeycomb release—rolled out today, with improved widgets that allow window resizing and scrolling. It also can now handle USB, so cameras and other devices such as keyboards, mice and game controllers can be plugged into Honeycomb tablets.

Android 3.1 will also be coming to Google TV this summer via the Android Market. Developers can now build Google TV applications with the Android SDK. Existing Google TV customers will receive this as an over-the-air update.

_

A books tab was added to the Android Market in February, and now Google is bringing the same experience to Android Market. Users can rent US$1.99 movies from Android Market and stream them to any device they’re logged into via their Google account.

Google also discussed its new in-the-works music service: Google Music. “When you add your music to the new service, you can listen on the Web through any device,” said Google executive Paul Joyce. “No syncing, no wires. You can stop worrying about where your songs are and start enjoying your music.”

Music Manager, a program for Mac and Windows, can sync iTunes libraries or MP3 folders with the cloud. Music on the Web is a full-featured music manager, with ratings, play counts and album covers. Playlists can be managed, with the information and music available on any device. It also allows the creation of playlists based on the user’s preferred songs, similar to Pandora.

Barra pointed out Android’s growth, from 500,000 devices in its first year to more than 100 million device activations in 2011, a figure released today. Last year, 100,000 Android devices were activated every day; today, that number is 400,000.

Android Market also has more than 200,000 applications available.

“What really matters is that the quality of these apps is amazing. The world’s most engaging, useful and entertaining mobile apps are running on Android. The most important thing for you, the developer, is the growth,” said Barra.