Android 2.2, aka FroYo, has begun arriving on Google Nexus One phones, ahead of its appearance on HTC's Android powered mobiles later this year.
Some Nexus One owners may already have Android 2.2, which is reportedly five times faster than its predecessor, as it is being delivered via an over-the-air update.
A statement from Google advised: "[You] will receive a message on your phone's notification bar. Just download the update, wait for it to install and you should be all set.
"This update will be rolled out gradually to phones - and most users will receive the notification by the end of the week."
HTC smartphones, including the Desire and Wildfire, will also be getting Android 2.2, although a specific launch date is yet to be confirmed, with current estimates suggesting arrival roughly in the third quarter of this year.
The search giant's announcement of the latest Android OS iteration appears to have been timed to regain the tech news agenda from Apple amid a surge of interest in the iPhone 4 and the new iOS4 operating system.