Google on Thursday started rolling out a new feature for its Gmail service: SMS messaging from the Gmail chat window in the left hand navigation pane.

The new feature is available through Gmail Labs, which can be accessed from a tab on the Settings page. It may not be immediately available to all Gmail users simultaneously, as is common when Google enables new features. Google expects to post an announcement on its Gmail blog late Thursday or on Friday.

To send an SMS message, a Gmail user simply enters an SMS-capable mobile phone number into the chat window and that prompts a "Send SMS" popup menu. Google's implementation of computer-to-phone SMS includes a particularly helpful feature: It assigns the Gmail sender a persistent pseudo-phone number so that the SMS recipient can send SMS messages back to the Gmail user at a later time using a consistent identifier. Typically, a computer user sending an SMS message to a mobile phone would create a different temporary identifier each session.

In the month of October, Google has launched seven new features for Gmail: Gmail Gadgets, emoticons for messages, Gmail for mobile version 2.0, Canned Responses, contact manager improvements, advanced IMAP controls, and Mail Goggles.

Gmail product manager Keith Coleman said that Google Labs has evolved into an increasingly significant mechanism for product innovation and testing at Google. After several years as a test bed for search and other products, the Labs concept debuted for Google's enterprise products about a year ago, for Gmail in June, and earlier this week for Google Apps.

"One of our goals with Labs was to set up a fast, iterative feedback cycle between the guys back in Mountain View coding this stuff and the users all over the world," explained Coleman.

In the past, Google's product development cycle would go something like this: Developers would create a new product, use it within their development group for a few months, launch it for internal use at Google, perhaps expand the user base to a group of trusted testers, and then finally release it to the public.