Google will continue expanding beyond its core search engine when it launches an instant messaging service with voice-over-IP capabilities today.

Google Talk, as the new program will be known, is beta mode and requires that its users have an account in Google's free Web mail service Gmail, due to the two being tightly integrated.

Industry observers have speculated for many months that Google would develop a consumer-oriented instant messaging service to compete against those from AOL, Yahoo and MSN.

To gain users, Google Talk will have to be a compelling service that has a comparable amount and type of "bells and whistles" the other IM services have, such as emoticons, as well as complementary applications, said Allen Weiner, a Gartner analyst.

"At a high level, this indicates that, whether it likes it or not, Google is officially a Web portal and a media company," said Allen Weiner, a Gartner Inc. analyst.

Google Talk will be built on XMPP (Extensible Messaging and Presence Protocol) framework, which could make Google Talk more attractive to developers than rival networks built on proprietary protocols.

To talk to contacts on Google Talk, users will click on a "call" button in an open chat window or by clicking on the phone icon next to names on the contact list. A user can have multiple voice sessions open but only one can be active at any given time.

Google Talk users' log in information will be the same they use for Gmail. Also, users will be able to access their Gmail inbox from within the Google Talk interface and send e-mails from there. Google Talk also will alert users about new messages received in their Gmail account.

Another point of integration is that users' Gmail contacts will be loaded automatically into their Google Talk interface, making it possible to exchange instant messages with those who have downloaded the IM software.

Google Talk users will also be able to invite those in their list of contacts to download the IM application and even contacts who aren't Gmail users will receive an invitation to sign up for the Web mail so they can get Google Talk.

Regarding the current lack of interoperability among the three largest consumer IM networks - Yahoo Inc.'s Messenger, America Online Inc.'s AIM and Microsoft Corp.'s MSN Messenger - Google said it is committed to work with IM service providers to establish links between its service and others.