Coaxial cable next to power lines, specially high volatge power lines is not a good idea. Not only will be very hard to keep the noise from filtering into the coaxial, the voltage that will ‘radiate” from the power line into the coaxial needs to be patch to ground every few poles to be sure that voltage does not end up on the equipment.
Fiber should be the perfect medium if you could afford it. Up to mile or mile and a half, you could use multi mode fiber, very simple to conectorize and handle. Over that distance you will need single mode fiber and muxing equipment.
If all what you want to transport is voice for several PBX ‘s, you could get your hands on very cheap muxes taht will transport E1 ‘s or T1 ‘s for the voice.
If the PBX only handle DS0 ‘s, that means 2 wire lines, you could still get a channel bank for each town and do drop and insert,using a channel bank to transmite and receive on each direction over the fiber link.
Or if you do not have the PBX ‘s yet, you will be better getting a PBX that will handle fiber optic .
There are several on the market that do that right now, and price is not as high as used to be.
This PBX ‘s have a central CPU unit, with all the brains, and remote cabinets, via fiber that are called expansions.
The added benefit of that is that you get a uniform dialing plan, with everyone being able to talk to everyone on the system.
If you need any aditional help, post your e-mail on the board and I will answer.