3CX IP PBX Windows Phone System

Here are some I found:

 

1-low cost =drive imaging (symantec backup exec system recovery (not backup exec), acronis, etc) ( 50-700 usd)
2-medium cost (if infrastructure in place)=hyper-v /vmware (thousand or two usd)
3-high cost=doubletake product, neverfail, windows clustering. (several thousand usd)

 

I have not tested option 2 and 3.