Batboard

I have a Motorola ASTRO mobile mounted at work. I would like to make a simple phone patch, one way.

I want to call a phone number, system picks up and keys radio, make an announcement, and hang up. Once the phone is disconnected, I want the radio to unkey.

ie:
RING
interface answers, keys radio
interface broadcasts any sounds coming across line
(end of message, system hangs up) interface unkeys radio, disconnects.

(Might be after 3 seconds of silence it disconnects)

Is there such an animal?

Sounds like an old Dial Access Paging Terminal (DAPT) of Zetron fame would do what you want pretty easily considering you only want one-way communications.

Thanks for the advice. I could use a cheaper solution, since I don't have multiple pagers, only a single need to key the radio.

A used DAPT on eBay (and they do show up often) shouldn't run you that much... And it's certainly less of a headache than engineering something else.