Searching http://www.dslreports.com/forum/voip may find some ideas.
Such as this older thread http://www.dslreports.com/forum/r240...sting-and-VoIP
(Note in that thread one poster RockyBB has since passed away, but was a wealth of knowledge on the forum.)

These days high search results on Google are often more important that dead tree directories.
Calling 411 I can see still being relevant

Goog411 went away
Perhaps the three alternatives in this post are worth considering: http://www.dslreports.com/forum/remark,24909978
(Not sure how easy it is to get listed in them?)