The US Federal Communications Commission (FCC) is to launch an investigation into Google's web-based Google Voice phone service after AT&T and others raised concerns that the web giant is blocking certain calls in rural areas of the US.

AT&T complained to the FCC in September that Google was blocking calls to numbers in rural communities because of the large access charges, undermining the principles of net neutrality. Access charges are the fees phone companies pay to each other to connect to their networks.

The FCC has now sent a letter to Google asking it to explain how Google Voice works and why it is blocking calls, a practice prohibited by the FCC.

Richard Whitt, senior policy director at Google, responded in a blog posting yesterday, declaring that the firm blocks certain calls because this is the only way to keep the service free of charge, and avoid "exorbitant" access charges.

"Google Voice is a free web application intended to supplement and enhance existing phone lines, not replace them," he wrote.

"The goal of Google Voice is to provide a useful, unified communications tool (including for, among others, soldiers and the homeless). Some have observed that Google Voice is 'something a real phone company should have offered years ago'."

Whitt added that the issue has nothing to do with net neutrality and that even AT&T in the past has asked to block calls to rural areas for the same reasons as Google.

"This is about outdated carrier compensation rules that are fundamentally broken and in need of repair by the FCC," he added.