Following some developer complaints of slow progress, Google on Monday released an updated version of the Android software development kit as well as a timeline for future releases.

In addition to fixing "tons of bugs," the update includes a "ton" of user interface changes, according to a blog post written by Dan Morrill, developer advocate at Google. It also includes new applications such as an alarm clock, calculator, camera, music player, picture viewer and messaging application.

Since Google first issued a preliminary SDK last November, it has worked closely with companies that are members of the Android Open Handset Alliance to further develop the Linux-based operating system, Morrill wrote. Now the companies are close to completing the first version of Android, which will be loaded onto devices shipping in the fourth quarter, he wrote.

Google also laid out a general timeline for future releases. In September, it could release additional SDK updates if necessary, and it expects to launch the final Android 1.0 software and SDK in either the third or fourth quarter. Also in the fourth quarter, Google plans to release the source code.

The updated SDK and timeline follow the recent submission to Google of an online petition signed by more than 200 developers. The developers asked Google to provide more information about when they might expect an update to the SDK, which they said was long overdue.

Google has angered some developers who say the company hasn't provided enough information about Android updates and accidentally revealed that it was offering an updated SDK to a small group of contest winners.

Separately on Monday, the U.S. Federal Communications Commission released documents approving HTC's Dream phone, a device widely rumored to become the first Android phone, for sale in the U.S. The phone could hit the market before mid-November.

Although no operator has publicly announced a definitive launch date for an Android phone, rumors have pegged T-Mobile as the first to sell such a phone.