ATIS and NTCA have been hounding the FCC as complaints went from about 100 a month in 2009 to over 1000 a month in late 2010. A group of them sent a letter to the FCC [pdf], which stated:
"the Rural Representatives identified a variety of concerns, including but not limited to: (1) calls that ring for the calling party, but not at all or on a delayed basis for the called customer of the RLEC; (2) calling parties who receive incorrect or misleading message interceptions before the call ever reaches the RLEC or the tandem it subtends; (3) calls that appear to “loop” between routing providers, but never reach the RLEC or the tandem it subtends; and (4) incorrect caller ID that displays to called parties."
Many carriers point the finger at their underlying network operator - another carrier that they dump the rural traffic on. MagicJack and Google Voice have a reputation for not completing calls to high expense rural areas.
The underlying problem is Inter-Carrier Compensation. Rural telcos not only get USF funds to operate, but also get many pennies per minute for call termination. IN comparison, RBOC's usually charge $0.005 for termination - a half a penny per minute. As traffic to rural increased due to businesses like FreeConference.com, many carriers including VoIP providers and cellcos, chose not to complete calls to those areas. It was getting expensive.
The FCC rules, "If carriers continue to hand off calls to agents, intermediate providers or others that a carrier knows are not completing a reasonable percentage of calls, or are otherwise restricting traffic, that is an unjust or unreasonable practice prohibited by section 201 of the Act."