Google on Wednesday began offering free and low-cost online phone calls to Gmail users in the U.S. through the integration of its Gmail and Google Voice services.

At a media event at its San Francisco office, Gmail product manager Todd Jackson, Google Voice product manager Vincent Paquet, and Google communications product manager Craig Walker recounted how Gmail has grown from an e-mail client into a communications hub that supports Google Talk instant messaging, video and voice chat, and now phone calls. 

"We have this communications platform between computers and phones," said Paquet. "Up until now, those platforms didn't communicate with each other, and that's what's about to change."

By integrating Google Voice with Gmail, Google may be able to help Google Voice avoid the fate of another one of its perhaps too innovative services, Google Wave. Gmail has hundreds of millions of active users and exposing them to the opportunity to make free and low-cost calls should encourage wider use of Google Voice. 

Google Voice was made available to the public in June after a lengthy period of closed testing. Walker declined to reveal current user numbers for the service; in June, Google said it had over a million active users of Google Voice.

Gmail users will be able to make calls from their Web browser -- provided there's a mic and speakers -- to the phones of people in the U.S. and Canada for free, at least for the remainder of the year, and at a low rate internationally.

"We're saving people a lot of money," said Walker. "The prices we offer this at are super-competitive."

According to a price comparison chart published by Google, a call from Gmail to a U.K. landline is billed at $0.02 per minute, compared to $0.021 plus a connection fee using a "leading Internet telephony provider," presumably Skype. A call from Gmail to a U.K. mobile phone is billed at $0.18 per minute, compared to $0.253 per minute plus a connection fee.

Walker said that Google is committed to maintaining free calls to the U.S. and Canada through the end of the year, and that the current plan is to maintain this rate. He said that Google believes it can make enough money on international calls to sustain the service.

Gmail users can make calls without a Google Voice account but cannot receive them; those doing so will appear to be calling from a generic number, which, if called, will promote Google Voice.

Paquet said Google was not ready to offer Gmail calling to business customers using Google Apps. While he would not explicitly state that Google is working on administrative controls to make the service manageable by IT administrators, he made it clear that Gmail calling for Google Apps users will appear eventually.

Gmail calling for users outside the U.S. is also under development and localized versions can be expected in the months ahead.

Walker said that Google continues to work aggressively to allow users to port their existing phone numbers to Google Voice. However, he was unwilling to commit to a specific timeline for availability.