Beware
We carried out some data processing work for a call centre company.
They invested hundreds of thousands of pounds into all new completely MS based comms kit for a new call centre. It never worked properly. There were several seconds delay in connecting calls and called people would hang up after 4-5 seconds of silence after picking up the phone. There were also other problems.
Over several weeks the comms providers tried everything - but nothing fixed the problems.
Result was that the company went bust - hundreds of people dumped out of work on the next payday - without being paid.
What's galling is that MS would have actually got their money for all the server licenses.
BTW - the old unix based systems had worked flawlessly for years - just some very flashy sales people persuaded the management that Microsoft/VOIP was the way to go forward.