I have set up a small PBX with a conference line.
There are a few options for connecting to it, the easiest option is calling from the PSTN. There are other ways to connect, but let’s keep it simple for now.
If you want to call in, the number is 549-4645, the default conference ID should be 2600. It should support 5 or 6 simultaneous calls, but I haven’t tested that theory. If there is interest in more capacity, I can see about adding more. It’s a local Cincinnati number, so you shouldn’t have a problem calling it from random phones around town, like unprotected wires that you have beige boxed.
It doesn’t make outgoing calls, so if you want to bring others in, you will have to use 3-way calling or the conference button on your phone. You get extra points for bridging in another conf, like Telephreak.
UPDATE 2/6/2017: The service is fairly stable now. If you are interested in an extension on the PBX, please let me know and I can get that set up. The difference between calling into the conf and having your own extension is that you can make calls to other extensions, including the conference, as well as make outgoing calls. Each extension also has a SIP URI for receiving pure VOIP calls.