Google is taking on internet telephone companies like Skype by allowing users to call from its free web-based email service.
The service allows users to make calls to land lines and mobiles from inside their Gmail account.
Phoning anywhere in the US and Canada will be free until the end of the year, while calls to the UK, France, China and Germany will cost 2 cents a minute.
Until now Google offered computer-to-computer voice and video chat services.
"This is a real big deal because now hundreds of millions of Gmail users can make phone calls right from their Gmail page," Craig Walker, product manager for real-time communications told BBC News.
"They don't need to download an additional application or anything to start making really high-quality low-cost calls. For the user it means much more efficient and low-cost communications."
The product will initially be rolled out in the US, the firm said. However, for a brief time, international users were also able to use the feature because of an error.
"Unintentionally we briefly made the service available to non-US English users," a spokesperson said. "We do hope to bring it to our international users soon"
When it rolls out the product link will appear on the left hand of the Gmail page within the "chat" window. A "call phone" option will pop up along with a number pad to let you dial the number of the person you want to talk to.
Google said money raised from international calls will pay for the free US and Canadian calls.
"What surprised me was that they actually said they hope to make money off the calls," said Danny Sullivan, editor-in-chief of technology blog SearchEngineLand.
"Normally Google is like 'We don't know how we are going to make the money' or 'We will make money down the way, don't worry about it' and this stands out as a big benefit that they get actual revenue early on."
Competition
Skype, which is the most successful internet phone offering, claims to have over 560 million registered users. The firm said 124 million used the service at least one a month while 8.1 million were paying customers.
The company is planning to offer shares to the public later this year. Observers said that it is too early to say whether companies like Skype should be worried.
"Skype is a well known company in this place and they are almost like a verb in the internet calling world in the way Google is with search. You Skype someone. So I think there is some inertia there to get over and I am interested to see how Gmail users respond," said Tom Krazit, senior writer with technology news site CNET.com.
"But you always have to worry when Google comes after what you do. They don't do things half way and bring a lot of resources to any problem they try to tackle. It doesn't mean you are doomed.
"Google's product won't work on your mobile browser so Skype has an advantage there but I don't think it is a stretch to assume Google will come out with a mobile version pretty soon," said Mr Krazit.
The company plans an eye catching way to get non-Gmail users to give the product a go. It is in negotiations with a number of university campuses and airports to install red telephone boxes around the country to give users the chance to dial and try.
