QUESTION AND ANSWER
Can I add an international number to a meeting already in session?
No, phone numbers can not be added after a meeting has been started. You will need to end the meeting, edit the meeting to add the appropriate number, and restart the meeting.
For how to add international numbers to your sessions see: https://na32.salesforce.com/articles/en_US/How_To/Add-An-International-Dial-In-Numbers-To-Your-Meeting?popup=false&id=kA8380000008Ohe