Thanks, BraveSirRobbin and Cobra.
I actually need nothing more than the ringing of the phone line for notification. No voice announcement or data needs to be transmitted as long as someone could later go to the alarm panel (or whatever) and find out which exactly contact was closed. Just need to know some switch was closed.
We'll call a dedicated extension on a IP PBX (asterisk) and the fact that extension Y is getting a call from Caller ID Z is all I need. It could be a SIP or analog connection to the phone system; both are easy to arrange. Later actions are already accomplished for human-made calls; I just need a simple switch to initiate the same actions from places that don't have/need a phone.
Notification is critical in the sense that it should be reliably trigger the phone call (I wouldn't want to kludge together something with untested knock-off relays from eBay) but the remote end isn't going to acknowledge the call in anyway so we don't have to call a bunch of contacts or redial if we don't get a response or anything like that.
I'm estimating eight switches right now but that could change in the future so some expandability is good. Money is a factor or we'd hire some contractor who'll probably come up with a worse solution anyway but there's money to do the "right thing" if that means spending a few hundred dollars more. The labor & cable to the switches will be far more expensive, even if it is just in terms of "free time" not spent doing other things.
(The Sensaphone actually looks pretty good - thanks for the suggestion! -- but is pretty much the same cost as an alarm panel based on some quick Google searches. Maybe its cheaper if I find an actual dealer.)