Google Voice blocks calls to certain rural areas because of outdated regulations that require the big phone companies to pay access charges to the rural companies when calls are completed in the rural company's phone network. The original idea behind this regulation was to help in sustaining rural phone networks that may not have enough subscribers locally to pay for all their costs. AT&T, Verizon and the rest of the big telcos have no choice about paying these fees. At the moment, Google Voice does have that choice. AT&T is not happy about that and has raised a bogus charge of Google violating net neutrality.??
It gets juicier. Some rural carriers figured out a lucrative business getting "popular" chat lines to use their local numbers. Each call that (mostly) men made to the (mostly) women at the chat service resulted in AT&T (Verizon, etc.) paying the access fees. This amounted to a lot of money. Enough money that the rural carrier chould just give the number to the chat service and in some cases kick back some of the wealth. In their defense, the rural carriers point to stimulating local economies, providing local jobs, and??American entrepreneurial spirit. (I made up the part about "entrepreneurial spirit." The local jobs would come from potential chat lines and tech help centers located in the rural area.)
Google's Richard Whitt says it best at the Google Public Policy Blog:??"This issue has nothing to do with network neutrality or rural America. This is about outdated carrier compensation rules that are fundamentally broken and in need of repair by the FCC."
Read Matthew Lasar's article, Is AT&T targeting Google Voice to stop "traffic pumping"?, over at ars technica for the deets.