Conference calls are used a lot by businesses and are a built-in feature of Asterisk and FreePBX (and therefore the distributions that rely on these – Trixbox, Elastix, PBX-in-a-flash …)
They are very easy to setup -
All you need to do is give it a conference number (which is just the same as an extension number) and a conference name, and that’s it. You can change the other settings as required such as having music on hold or a message when users join the conference. You can put a password/pin on the conference which is probably a good idea.
Once you save your conference you will be able to dial it from an internal extension or use it as a destination for an Inbound Route or IVR
I’ve seen reports of people having over 20 callers in a conference which is probably more than most poeple could ever need!