Hi,
First find out if Calling Plans are available for your country (Australia, Belgium, Canada, France, Germany, Ireland, Netherlands, Spain, United States (and Puerto Rico).
The full list is here if any new countries will be available
https://docs.microsoft.com/en-us/microsoftteams/country-and-region-availability-for-audio-conferenci...
Then you have to buy Calling Plans licenses, you can select a Domestic Calling Plan or a Domestic and International Calling Plan. In these license there is a number of calling minutes includes, ex. in Domestic Calling Plan for Germany you can dial out 1200 minutes to German phone numbers. You can also add Communications Credits and these are shared within your organisation so a user with a Domestic Calling plan use these credits when calling international numbers.
https://docs.microsoft.com/en-us/microsoftteams/calling-plans-for-office-365
Then you can assign a new number or transfer an existing number.
https://docs.microsoft.com/en-us/SkypeForBusiness/what-are-calling-plans-in-office-365/getting-phone...
When this is up and running your users should be able to start calling, but you should also setup Emergency addresses and numbers, and create dial plans.
If you are not in a supported country you can use CCE (Skype for Business Cloud Connector Edition) or maybe better in that case is to move to Teams and use a Direct Routing Gateway.
https://docs.microsoft.com/en-us/skypeforbusiness/skype-for-business-hybrid-solutions/plan-your-phon...
Keep in mind that Skype for Business Online will be replaced by Teams some time in the future so when you are done with testing and educated all your users it might your turn to move to Teams so you should think of starting this in Teams instead. The steps for getting numbers with Calling Plans are the same for Teams.
