Hi CJ,
Welcome to the forums.
If the rates and quality are in place, I would see no issues with using Google Voice, as long as you go into it with your eyes wide open, I commented about free services previously at
http://pbxinaflash.com/forum/showthread.php?t=7572, causing some upset and disagreement.
The main issue I may have, is that carriers with whom I have dealt with in the past have someone you can speak to when things go awry, whereas with Google's services, I'm not sure there is a number you can call and speak to a knowledgeable engineer to help you solve your issues.
Joe