I sent both
voip.ms and CallCentric email asking to clarify their pricing/policy for (primarily) e911 services.
voip.ms will not allow you to have e911 without first getting a phone number from them. So, you pay $0.99 - $2.00/mo for a phone number (variation depends on where you are located) + $1.50/mo for e911 services. Total $2.49 - $3.50/mo. There is a one time setup fee of $1.50 for 911 plus $0.50 for the account.
Also,
voip.ms will not pass your (external) caller-id info to the call center, they pass their internal number instead. This is, of course, registered with the call center so they know it is associated with the right address.
CallCentric will allow you to get e911 without charging additionally for the number. Their 911 service is 1.50/mo which you can get along with their Pay Per Call plan. They also will not pass external caller-id info. As far as I can tell there are no one time set up fees, but I am not 100% sure about that part.
Tom