Thanks for the response Stefano.
These are physical phones - Polycom 311 - however I also tried to initiate a call from the PureCloud App and received an Edge communication error. I did not try a WebRTC call.
I was running a Ping during the circuit flip and we didn't even loose a ping. I did have a call going during the flip and it did not drop.
This was an initial quick test and I will schedule another longer test over the weekend. We are building a Contact Center and need to have as seamless a failover as possible.