If you are using Cloud PBX with PSTN Calling, you will receive your telephony services from Microsoft. To assign phone numbers to your users, you can either port in existing numbers or acquire new numbers from Microsoft - however the process in doing so will vary from country to country. As we are looking to add new countries and continue to improve our processes, we want to point you to the official documentation that has not only all required information but will also be always up-to-date: Get phone numbers for Skype for Business Online
So in order to avoid any surprises, whenever you start using Cloud PBX with PSTN calling in a country where you have no prior experience, be sure to visit the official documentation page and review your country specifics.
If you have any questions or comments, feel free to let us know in the community!