It bothers me that the VOIP providers don't, say, play a special message explaining the issue. If it's not illegal for them to block these numbers, then why not at least explain themselves? Perhaps they could offer at-cost connections? "Press 1 if you are willing to pay $0.08/minute for this call"
I agree that a message would be helpful. I've learned to blindly accept it as an isolated technical issue. I'm accustomed to grabbing my cell for conference calls now.