This video shows how you can add a virtual ShoreTel IP Phone appliance into your existing ShoreTel environment to provide 99.99999% up-time and a N+1 redundancy.
The cost is the best price, as long as you have room and resources on a VMHost, $0. This Virtual spare provides failover for all your ShoreTel sites. In the event that a ShoreTel switch does go down, the virtual Spare will accommodate 250, 500 or 1000 IP resources (depending on resources configured) for your phones to failover. You then have 45 days to replace the down switch and move all the users back to their home switch. At that point the license compliance screen stops pestering you and goes back to quiet.
The minimum requirements are ShoreTel release 14.2 or greater and ESX 5.1 or greater.
Find more ShoreTel and Mitel technical tips HERE