I have a FreePBX servers with a spare FXS port. I also have a legacy analog, 1-way overhead paging system with all the wiring intact (I believe) and speakers. What would be the lowest barrier to entry method (cost and setup time) to set this up?
What type of paging hardware do you have?
You need a paging gateway. This device will answer the call made to the FXS port and convert that to the type of input on your paging amp. I have used Bogan UTI-1 and Viking CPA-7B for this. You can probably pick one up for about $150.00 USD. Valcom also makes good stuff.