I think that this is part of the confusing way they sell it. You can use outbound Microsoft numbers (similar to how Skype calling used to work), but if you want

I think that this is part of the confusing way they sell it. You can use outbound Microsoft numbers (similar to how Skype calling used to work), but if you want inbound numbers I think you need a third party telco? These products form the Calling Pack (Microsoft) and the Voice Service (Telco) respectively, and then on top of that you need some kind of bridge (Telco) if you want to have a 13 or 18 number. And if you want to have your outbound number recognisable as your inbound number, that’s another aspect of the Voice Service that needs to be configured. Unfortunately the latter infrastructure doesn’t live at MS and it can be really unreliable if the telco hosting it is small. Our phone goes down for around an hour once a week or so.