If you are on Voice Ops listserve, you have seen an interesting thread about Rural Call Completion. The FCC has tried to tackle this problem, but there is too much money in rural calls still.
VZ has devoted a couple of bucks to it, according to a telecompetitor article with some good links. VZ has also set up a RCC Hotline number: (800) 285-3776.
The VZ Policy Blog has the details about the RCC workshop and plan.
Speakeasy has a blocked list. NOTE: 'Regarding the reference to the Speakeasy link - thank you for bringing this page to our attention. Please be advised that Speakeasy was acquired by MegaPath in 2010. MegaPath does not block rural calls. The link you have referenced is outdated and inaccurate. We are removing that page from the legacy site. We apologize for any confusion."
Personal notes from many on the list suggest that many VoIP Providers block exchanges, especially to traffic pumpers.