It can be tempting to start talking when you have something to say on a conference call, but it is important to wait your turn and avoid the temptation to interrupt the person currently speaking. The reasons for this are actually two-fold:
First, there are some conference bridges that are configured only allow one person to talk. As such, if you begin talking while someone else still has the floor, there is a good chance that you may unknowingly cut the speaker off before they are done speaking. Second and more importantly, waiting your turn is really a simple matter of politeness and conference call etiquette.