Google on Wednesday began adding Internet telephone capabilities to its free Web-based email service in the United States.

Gmail was infused with Voice, a Google telecommunications service that lets people use a single telephone number for all of their phones.

"Starting today, you can use Gmail to receive or place Google Voice calls," software engineer Nick Foster said in a blog post.

"We're rolling out this feature to US-based Gmail users over the next few days."

A "call phones" option in Gmail chat will enable people to make, screen or field Voice calls at their computers using Gmail, according to Foster.

The engineer said that Google "took great care to make sure that our rates are as low as possible" for outbound calls from Voice numbers.

Calls to landline numbers in France, Argentina, Britain, or Hong Kong cost two cents per minute, according to a Google rate chart.

Voice reportedly attracted more than a million users during an invitation-only test phase before Google made the service available to anyone in the United States in late June.

Along with letting users have one phone number that rings at all of their telephones, the service converts voice mail or text messages into email and allows for toll-free calls to the United States and Canada.

In an online video describing Voice, Google promised "less annoyances and more awesomeness - for free." Voice threatens to challenge global Internet telephony star Skype.

Google promises that the service works "no matter what kind of phone you have or which carrier you use."

People in the United States can sign up for the service online at or visit for information about tying it to their email accounts.