You may have been on a Teams meeting and heard the rather annoying entry and exit sounds. They can be “+4412343434 has joined the meeting”, or playing the recording name of the joiner or just tones.
Announcing out the name or phone number can be important if you are having a highly secure meeting, but mostly I find the entry and exit announcements disrupting to the meeting.
Fortunately, you can turn them on and off.
Head to the Teams and Skype Admin Center (direct link, https://admin.teams.microsoft.com/ )
Meetings / Conference Bridges / Bridge Settings
You can set to entry and exit tones or reading out names or numbers
Or you can turn them off completely