Microsoft Teams meetings are great for online collaboration, but many organizations still need reliable telephone “listen-only” access, especially for large broadcasts where attendance can exceed Teams’ dial-in or meeting limits (often cited around 250 for certain meeting scenarios). By connecting a third-party conference call service like Vast Conference which supports up to 5,000 ports, you can offer a dedicated, high-capacity phone bridge for audio-only listeners, reduce strain on the Teams meeting, and make it easy for participants to join from any phone (no app, no headset, no strong internet required). This approach is ideal for town halls, investor calls, training sessions, and public-facing briefings where you want Teams for presenters and screen sharing, while Vast handles high-volume telephone listen-only attendance.
How do I connect a conference call to a Microsoft Teams meeting?
This setup lets you use Vast Conference as a high-capacity, listen-only telephone bridge while Microsoft Teams remains the host meeting for presenters, screen sharing, and collaboration.
What you’ll need
Vast Conference dial-out (to call the Teams dial-in number)
Waiting Room (to hold callers before the meeting begins)
Online Web Interface (to manage mute/unmute and move participants)
Recommended conference call settings (listen-only)
To keep phone attendees listen-only and reduce distractions, configure your Vast conference with:
Lecture Mode: ON (all callers join muted)
New Entry Tone: OFF
Waiting Room: ON
Doorbell/Waiting Room chime: OFF
Dialing out from the conference call to MS Teams meeting
Step 1: Join your Vast Conference as host
Dial into the Vast Conference phone number.
Enter your 6-digit conference code.
Enter your 4-digit host code.
Step 2: Dial out from Vast to the Microsoft Teams meeting
From the host phone keypad, initiate dial-out by entering: 67*
When prompted, enter the Microsoft Teams dial-in number, then press #.
When prompted, confirm by pressing 1.
Enter the Teams conference ID (follow any prompts to complete the connection).
If Teams uses a lobby/meeting admission setting, allow the dialed-in number to be admitted.
Rejoin the Vast Conference host controls by entering: 68* from the host telephone.
At this point, your Vast call is now connected into the Teams meeting by telephone.
Step 3: Configure audio so Teams is the only unmuted line
Mute the host telephone (so your host line does not add noise/echo).
In the Online Web Interface, locate the participant that represents the dialed-out Teams connection.
Unmute only the Teams-connected participant line (this becomes the audio feed into Teams).
Keep Lecture Mode ON so all other phone participants remain muted (listen-only).
Step 4: Start the session (move callers in when ready)
When you’re ready to begin, use the Online Web Interface to move callers from the Waiting Room into the Main Conference.
Once the session begins, you can turn Waiting Room OFF to allow late joiners to enter directly (optional).