999 or 911 ie: emergency calling needs to be addressed. Many TA's can be setup with an address. Like cell users on the move would need to remember that.
With many many people building servers another thing that needs to be considered is "inter-connection" into other SIP networks. That will allow you to offer a wider area of free caller to caller services. There is safety in numbers. Like the Internet started peering agreements between networks will be key to expansion. My group is taking the lead in peering agreements. We will peer with any VOIP SIP network no matter how big or how small. All you have to do is email: voip@livevoip.com We plan on making our free services like calling USA 800#'s available to anyone who is peered with us.
The future of this business is what we all make it.
Mike French LiveVoip LLC