Microsoft is new to the phone business. The below link is a description of their product. You decide if that suits your customer:

https://techcommunity.microsoft.com...ble-in-the-u-s-on-april-1st/ba-p/1231698

You have like hundreds of choices when it comes to cloud. Choose wisely, a-lot of hucksters out there.

We've had mixed results with Mitel cloud. NEC seems to have very good products and support.