It's pretty simple. Take the other port on your ATA-186, and hook it up to a Valcom V-9924C (www.valcom.com) or a Bogen NR100 (www.bogen.com). Put it in a pickup group, and then you can do a group pickup from whatever phone to pick calls up off the night ringer. Or, if you only want to pick it up from a couple phones, you could share the ATA-186 DN on a line on those phones. If you go with group pickup, any phone you pick up from needs to have a pickup group assigned to its line.
CallManager does have kind of a silly restriction that a phone that wants to do a Group Pickup has to be a member of a pickup group, any pickup group. If you need to be able to pick up from any phone, what I do is make a magic unused pickup group and put it on every line that doesn't already have a pickup group, and use the Softkey template editor to remove the Pickup button from phones that aren't in a "real" pickup group. That way you don't have issues with people accidentally picking up random calls ringing elsewhere.
Those boxes shown above will generate line-level audio ringing sounds from the FXS ring signal generated by the ATA-186. Either of those units will connect to the line-in or music inputs of your Bogen paging amplifier. Some Bogen paging amplifiers will actually accept the FXS ring signal directly, I think, without any extra hardware. That does of course depend on your exact model. Bogen has lots of documentation posted online, as does Valcom, so check that first. If you order either of those, make sure you order them with the appropriate (not included!) power supplies.
