The voice-enabled IM service actually went live on Tuesday afternoon, according to blogger Ben Guild, who was able to log on around 5:40 EDT.
The new service marks another step on Google's evolution from search service to Internet gateway.
The free Google Talk service lets users initiate text or voice chats from a stripped-down interface. The service is integrated with Google's free e-mail service, Gmail, so that, when a Gmail user downloads the IM application, it's instantly populated with that person's Gmail contacts.
''It will be easy to install, uncluttered and very fast to start up,'' said Georges Harik, Google product director.
''All Google's competitors have this kind of capability or are developing it; maybe out of necessity, Google needed to develop IM and VoiP,'' said Kelsey Group analyst Greg Sterling.
Yahoo Messenger launched a PC-to-PC voice chat feature in 1999. In August 2005, it launched Yahoo Messenger with Voice, which is based on SIP and includes voicemail. AOL launched a consumer version of its AIM Voice Conferencing service in December 2004.
Sterling said it was natural for Google to combine IM and VOiP, but interesting that it tied them into e-mail. ''If you adopt this, you need to sign up for Gmail, which will drive Gmail adoption as a byproduct of the popularity of this,'' he said.