said by w1ve:
Actually, voip.ms keeps images of each site, and can bring any site up anywhere by using BGP. So, newyork.voip.ms can be rerouted to come up in a server in LA -- without DNS changes.
At the risk of being labeled a voip.ms hater for correcting this, actually what you've stated here isn't true for them.
Their servers are in the middle of shared address space advertised by their hosting suppliers. The smallest route that will be accepted on the public Internet is a /24, so for that to ever happen all other server customers on those subnets would have to move facilities with them.
They can recover using DNS as was originally stated, and that is a perfectly valid recovery method that is used by nearly every company in the industry from Amazon to Zappos. While maintaining the IP address does present benefits for things like firewall rules, it presents complications with concurrent operations and testing failover scenarios that ultimately make the option LESS reliable than simple DNS failover.