The PIN number may change between launches of the same conference.
When you join a BigBlueButton session, you will see a dial-in number and PIN number (such as 39320 as shown below).
BigBlueButton will attempt to keep this PIN number consistent between launches of the same conference, but it is not guaranteed to be consistent.
In other words, if you copy this information from a previous session and send it out to other before starting the same session again, the PIN number may change.
If you have users that want to join the meeting by phone, the safest approach is to start the conference a few minutes earlier and then e-mail them the current dial-in number and PIN number.