Many companies are using Office 365 with Enterprise Voice. This also provides Skype for Business and all UCC features. There is, however, a snag with this solution from Microsoft known as "Cloud PBX": the functions can only be used within the company. But employees also want to reach external contacts and be reachable for them, as they are used to from the existing PBX telephone system. This is not automatically possible for Skype for Business, which is integrated in Office365, as it does not have access to the PSTN (Public Switched Telephone Network). However, only access to the PSTN enables Skype4Business users to call any telephone numbers worldwide.
