SAN FRANCISCO – Google Inc. is adding a free e-mail feature that may persuade more people to cut the cords on their landline phones.

The service unveiled Wednesday enables U.S. users of Google’s Gmail service to make calls from microphone-equipped computers to telephones virtually anywhere in the world.

All calls in the U.S. and Canada will be free through at least the end of the year. That undercuts the most popular PC-to-phone service, Skype, which charges 1.2 cents to 2.1 cents per minute for U.S. calls. It also threatens to overshadow another free PC-to-phone calling service called MagicTalk that was just introduced by VocalTec Communications Ltd.

Skype, Google and many other services have been offering free computer-to-computer calling for years.

Google hopes to make money on its PC-to-phone service by charging 2 cents or more per minute for international calls. The international rates will vary widely, sometimes even within the same country. Google posted a rate chart at https://www.google.com/voice/b/0/rates.

People also will be able to receive calls on their PC if they obtain a free phone number from Google or already have one.