Firstly, what is a PBX? A PBX (Private Branch Exchange) is a company’s telephone system. Historically it was mostly based on hardware and located on site.

Cloud PBX is, in simple terms, your phone system in the Cloud. It’s Microsoft’s technology for enabling call control and PBX capabilities in the Office 365 cloud via Skype for Business Online.

Now users can use Cloud PBX to take care of basic telephone call control tasks: They can make, manage and receive calls, at work, home and on the road using which ever device they wish – phone, laptop, mobile devices etc.

Calls within your organization are handled by Skype for Business. Skype for Business (offered as part of the Microsoft Office 365 package) has become a popular method of communicating within and between companies, but until recently didn’t offer the telephone functionality.

To enable calls outside your organization, you would need to be connected to the PSTN (public switched telephone network). There at two ways you can do this:

  1. Purchasing the PTSN Calling service add-on to Office 365

This is an add-on to Office 365, and means users will be homed in the cloud with no on-premises server deployment required. PSTN Calling allows you to search, acquire, and assign phone numbers to users in your organization so that users can make and receive phone calls with people inside and outside of your organization. There are international and domestic subscriptions available.


  • Cheaper and faster to get started.
  • Pay one bill for all your communications.
  • All the latest updates delivered automatically.
  • Pick new numbers or port existing numbers.
  • No need for any server software on-premises.
  • Easier to administer.

PSTN Calling

  1. Using on-premises PSTN connectivity

This is where software on-premises connects with your existing telephony infrastructure. Your users are homed in the cloud and are enabled for Cloud PBX, but their calling is processed through software on site.


  • Take advantage of existing comms infrastructure.
  • Retain your carrier contract.
  • Simply migrate users from on-premises to cloud.
  • Preserve customization in Server deployment.
  • Significantly smaller HW footprint onsite.

On-Prem PSTN Connectivity

One of the options with on-premises PSTN connectivity is Skype for Business Cloud Connector Edition. Cloud Connector is a set of packaged Virtual Machines (VMs) that implement on-premises PSTN connectivity with Cloud PBX. This hybrid offering is designed for organizations that want to enable their Skype for Business Online users to use their existing on-premises PSTN connection, with Skype for Business call control in the cloud.

The right Cloud PBX option for you very much depends on your current set up and whether you want to connect to your existing infrastructure.

At 1plex we have both the PSTN Calling Option and Cloud Connector Edition available to demo. If you would like to book a demo or to discuss the best options for your organization, please Contact Us to book an appointment.