Google Inc said on Wednesday it restricts calls to less than 100 U.S. telephone numbers with its Google Voice service, responding to a query from the U.S. Federal Communications Commission.
Google Voice has been surrounded in controversy since its launch in March.
Google has said that Apple Inc rejected the Voice application for the iPhone, while Apple has maintained it is still studying the software.
In addition AT&T Inc complained to the FCC that the service was restricting calls to some users.
Earlier this month, the FCC asked Google to explain how the service blocks expensive calls to some rural areas, after lawmakers demanded an investigation.
Google Voice allows consumers to make low-priced calls by routing portions of the call over Google's infrastructure and the Internet. It also offers a variety of enhanced voicemail management features,
The FCC had set a deadline of Wednesday to respond with information about how Google Voice calls are routed, why it restricts calls to particular telephone numbers and how Google chooses the numbers.
In Google's response, which was posted by the FCC, the Internet search leader said it began restricting calls in August. The company added in a blog posting that it has for the past few weeks been working to refine its system for blocking calls.
Google said fewer than 100 numbers are restricted, all of which the company said it believes are engaged in high-cost traffic pumping schemes such as adult chat and free conference call lines.
The Voice service is available to a limited number of people. In June, the company said it began noticing extremely high cost calls to a concentrated number of destinations.
In the blog posting, Google explained it has developed a method of restricting calls to specific numbers that were exploiting the service.
(Reporting by Gabriel Madway; editing by Andre Grenon)