Google's response(PDF) to the FCC’s inquiry regarding Google Voice blocking calls to some numbers says it is only blocking about 100 numbers.
AT&T with it's crystal clear record (AT&T also whined last year about expensive calls to rural numbers doing traffic pumping) tried to undermine Google's efforts with its voice service and even Google's web efforts. There were many exchanges of communication between AT&T, FCC, and FCC, Google over Google Voice’s blocking of high-cost “traffic pumping” schemes, like adult chat and “free” conference call lines.
According to Google
555-555-XXXX -- generated more than 160 times the expected traffic volumes, and accounted for a whopping 26 percent of our monthly connection costs.Basically talented Googlers are devising ways to block specific numbers that engage in traffic pumping schemes and expensive sex lines.
Google also told FCC about fixing the broken carrier compensation system and pressing need of reform.
I hope AT&T also lays off get it's act together and service it's customers better, like Google does!
Google Public Policy Blog: Our response to the FCC on Google Voice