Phone Amplifier

I am an EE but don't have any experience in audio circuits so I was hoping somebody could/would help. Here's what I'm looking to do, my dad has a large model train layout in his basement (about 85' by 30') and has 4 towns spread out with a central dispatchers office. We would like to set up a phone system between all 5 locations. It would just be a party line and when you pick up the phone you just start talking. I have the handsets and a simple amplifier circuit that I found but the noise on the lines makes it unusable. Currently the 4 towns have 4 conductor phone cable home run back to the dispatchers office. So in a nutshell I guess I'm looking for a circuit that can power up to 5 phones and provide useable audio. Thanks!

Shawn