By Katie Marsal

Published: 09:55 AM EST

Though the absence of Google Voice from the iPhone App Store previously prompted an FCC probe, a group of lawmakers now want the service itself investigated for blocking calls to rural areas.

AT&T, the exclusive carrier of the iPhone, has complained that Google Voice would have an advantage over other carriers if is not required to follow the same rules as other telephone service providers. Currently, Google's telephony service has the ability to block calls to rural areas where it is more expensive to connect. Federal law prohibits traditional U.S. carriers from blocking such calls.

According to Reuters, a bipartisan group of 20 legislators from rural areas in the U.S. House of Representatives wrote a letter to Julius Genachowski, chairman of the Federal Communications Commission, to investigate the matter.

In September, AT&T wrote a letter to the FCC over its proposed rules for net neutrality. The nation's second-largest wireless carrier argued that Google must comply with the same regulations AT&T must if it plans to compete with traditional telephone operators.

The FCC has already investigated both AT&T and the Google Voice service after Apple refused to accept Google's Voice application into the iPhone App Store. AT&T has denied any role in the program's non-acceptance.

Apple has said that it alone has not accepted the Google Voice application. It has justified that decision by stating that the software too closely replicates the core functionality of the iPhone.

After AT&T, Google and Apple all filed formal letters with the FCC over the matter, discrepancies in each company's version of the events arose. Google claims that Apple outright rejected its application from the App Store, while Apple has countered that it has simply not accepted the application, but continues to review it.

Following a recent push by Genachowski, the FCC chairman, to preserve Net neutrality on all networks, including wireless, AT&T responded by announcing it will allow voice over IP calls via its 3G data network for iPhone users.