In response to a Federal Communications Commission letter prompted by an AT&T complaint, Google says limits on Google Voice calls are due to exorbitant rates.

FCC Wireline Competition Bureau Chief Sharon Gillett asked Google on Friday to explain how it decides which calls to block and noted that telecommunications companies are prohibited from such activity.

AT&T says the limits give Google Voice an unfair advantage.

While Google admits to having a policy that restricts Google Voice calls to phone numbers in a small number of rural areas, Google counsel Richard Whitt explained why they made this decision.

Telecom providers not only charge exorbitant termination rates for these calls, but they also partner with adult sex chat lines and 'free' conference calling centers to drive high volumes of traffic, Whitt said, according to MacWorld.

Google Voice is a free application and we want to keep it that way for all our users -- which we could not afford to do if we paid these ludicrously high charges.

The search giant said in a blog post on Friday that it shouldn't be subject to the FCC rule because Google Voice is a software application that is meant to supplement and enhance existing phone lines, not replace them.

Google implied that AT&T is being hypocritical in asking for FCC action because it has sought to block calls to those areas.

AT&T said it merely wants the rules equally enforced on all phone service providers.