Skype for Business PSTN Conferencing

Office 365

Applies to: Office 365

Topic Last Modified: 2016-09-20

In Skype for Business, a PSTN conference – commonly known as a dial-in conference – is any conference in which at least one participant dials in to the audio portion by using a PSTN (public switched telephone network) phone. The ability to use a phone to access a meeting is useful for individuals who are on the road or otherwise cannot attend a meeting using a mobile device or PC. Using a phone also can be a better option in other scenarios, such as when internet connectivity is limited or when a meeting is audio only.

With Skype for Business PSTN conferencing, users in your organization can host or create meetings that contain dial-in phone numbers. Callers can then use those phone numbers to call into a meeting using their phone (users who are dialing into a meeting will only get audio, not instant messages, shared desktops, or files being shared in the meeting). You only need to set up dial-in conferencing for users who plan to schedule or lead meetings. Unless the organizer has locked the meeting, anyone who has the dial-in number and conference ID can join the meeting. For details, see Getting started with dial-in conferencing and Dial-in numbers available for dial-in conferencing.

In Office 365, you can enable dial-in conferencing either by using Microsoft and Office 365 as your dial-in conferencing provider, or by using a third-party dial-in conferencing provider (also called an audio conferencing provider, or ACP).

When you are setting up and configuring dial-in conferencing, you can select the primary and secondary (up to 4) languages that are used when callers dial in to a meeting. For a list of supported languages, see Dial-in conferencing supported languages.

PSTN conferencing is not available in all countries or regions. For a list of the countries or regions in which you can purchase PSTN conferencing, see Where can you get PSTN conferencing?.

PSTN Conferencing currently is not available for Office 365 nonprofit plans.

The ACP gives the toll, toll-free, and international phone numbers that users will dial into and that are included in the meeting invitation. It also sets the language that users will hear when they dial into the meeting; creates conference IDs that are used to join a meeting; and provides your organizer with a PIN to start the meeting over the phone. Your first decision in implementing dial-in conferencing is which audio conferencing provider (ACP) to use: Microsoft or a third-party provider. Using Microsoft as the ACP has many advantages over a third-party ACP. For details, see Dial-in conferencing in Office 365.

A single user can only use Microsoft or a third-party ACP as their dial-in conferencing provider, but not both. An organization can have some users that are using Microsoft and some users that are using a third-party ACP.

To learn how to assign Microsoft as the ACP, see Assign Microsoft as the dial-in conferencing provider to a user. To learn how to assign a third party as the ACP, see Assign a third party as the dial-in conferencing provider to a user.

You can also switch from using a third-party ACP to using Microsoft as your provider. For details, see Changing a user from a third-party ACP to Microsoft as the dial-in conferencing provider

Maximum number of phone participants per meeting: 250

The maximum length of dial-in conferencing meetings depends on who is in the meeting and the type of authentication they used to join it, as shown in the following table.


Meeting attendees

Meeting end time

There are users who have joined using a Skype for Business client, or have dialed into the meeting

The meeting ends if there are no changes to the attendee list after 24 hours

All of the users are dialed into the meeting, but someone has used a PIN to enter the meeting

The meeting ends after 24 hours

All of the users are dialed into the meeting, but no attendee used a PIN to enter the meeting

The meeting ends after 24 hours

For more information about meeting limits, see Skype for Business Online Limits.

The following table shows which types of PSTN conferencing are included in the plan and which are billed on a per-minute basis.


PSTN conferencing

Included in plan

Tolled dial-in conferencing


Toll-free dial-in conferencing


Tolled dial-out conferencing

Dial-out to Zone A countries (listed below) is included during the introductory period.1, 2, 3

Dial-out to any country outside of Zone A is not included.

Zone A countries:

Australia, Austria, Belgium, Brazil, Bulgaria, Canada, China, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, India, Ireland, Italy, Japan, Luxembourg, Malaysia, Mexico, Netherlands, New Zealand, Norway, Poland, Portugal, Puerto Rico, Romania, Russia, Singapore, Slovak Republic, Slovenia, South Africa, South Korea, Spain, Sweden, Switzerland, Taiwan, Thailand, United Kingdom, United States

1 Subject to misuse and fraud controls.
2 Subject to Skype for Business Online PSTN services use terms.
3 At the end of the introductory period, international dial-out minutes will not be included in the plan (they will be charged), and domestic dial-out minutes will only be included in the plan for a specific set of countries. For more information, see Skype for Business Online PSTN services use terms.

For a list of common questions about the dial-in conferencing included in Office 365 and Skype for Business, see Dial-in conferencing frequently asked questions (FAQ). For known issues, see Dial-in conferencing known issues.

For information about licensing options, see "Skype for Business Online Meeting Broadcast and PSTN Services Licensing Options" in Skype for Business Online Service Description.

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