Perhaps an entirely different solution -
You could just use an external analog (or SIP) ringer, or even any other phone(s) with a different sound. Just configure the hotline to dial a second ring group that includes the extra phones or ringer. We have evening calls set to ring over our paging system, for example, but any alternate ringer would be sufficient. Granted, if this involves many separate areas, then you'd need an alternate sound and device for each...
Just a thought.
-dg