AT&T told government regulators that Google's Internet-based telephone service violates rules prohibiting telecom companies from blocking any legal call.

AT&T's allegations were contained in a letter sent to the Federal Communications Commission on Friday. The letter, which was posted by The Washington Post, claims Google Voice violates FCC regulations by blocking calls to certain rural communities where carriers charge high fees for network access.

The invitation-only Google Voice provides people with one telephone number for receiving calls from multiple numbers, including landlines and mobile phone. The service also manages text messages and voice mail.

AT&T said the restrictions imposed by Google gives its service an unfair advantage over competitors by avoiding the high fees others have to pay.

"By blocking these calls, Google is able to reduce its access expenses," AT&T said. "Other providers, including those with which Google Voice competes, are banned from call blocking."

In a blog, Google acknowledged blocking calls, but said the FCC rules do not apply to its service. That's because Google is only providing a free Internet application. In fact, a person needs to be a customer of a carrier in order to use Google Voice.

"Google Voice is not intended to be a replacement for traditional phone service -- in fact, you need an existing land or wireless line in order to use it," Richard Whitt, a telecom and media counsel for Google, said. "Importantly, users are still able to make outbound calls on any other phone device."

AT&T and other long-distance phone companies tried to block calls to certain local carriers in rural areas, but were ordered to stop by the FCC in 2007. The commission ruled that preventing someone from making any legal call would degrade the reliability of the nation's telecommunications network.

Besides violating the FCC's rules against call-blocking, AT&T argued that Google is also going against the principle of "net neutrality," which Google and other Internet companies champion. Net neutrality is a term applied to a proposal that would require Internet service providers to offer unrestricted access to their networks. However, telephone companies and other ISPs argue they need to be be able to control traffic in order to maintain quality service to all customers.

FCC Chairman Julius Genachowski is expected to deliver a speech Monday that will lay out broad rules supporting net neutrality. Genachowski's speech is expected to be delivered during his keynote at the Brookings Institute.

Google said net neutrality should not be considered in the AT&T complaint, because the FCC does not have jurisdiction over how software applications function. "AT&T apparently wants to use the regulatory process to undermine Web-based competition and innovation," Whitt said.

Nevertheless, AT&T closed its letter arguing that the issue comes down to having a level playing field for all companies to compete.

"The Commission cannot, through inaction or otherwise, give Google a special privilege to play by its own rules while the rest of the industry, including those who compete with Google, must instead adhere to Commission regulations," the letter said. "We urge the Commission to level the playing field play by the same rules as its competitors."

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