I am speaking a little out of turn here seeing as I don't have a lot of experience in this field (overhead line suspension) but I do have a little bit of clue, and thus will throw in my thoughts (which may be worthless).
There are two ways to do this. One is to use an Industrial twisted pair control cable, and using metal straps of some sort secure it to a steel cable which is then secured and tensioned to the poles.
The other, easier, and more correct way of doing it is to use variable lay twisted pair overhead suspension phone wire. These cables normally come in a minimum of 6 pairs and three common guage sizes for this wire are 24, 22 , and 19 (at least in what I have seen). I don't know what distances you are running, but you will probably want 22 guage, but do your own math on that one.
With that wire (
an example here) You buy the wire, special clamps which secure to the messenger wire and the pole(S) and whatever splice boxes you may need.
A warning: This stuff is not cheap, but is designed to last and engineered to work in these type of environments. In any case, I would probably recommend transformer isolation and line drivers on any sizable run.
Again, consider the source of who this came from, but maybe it will give you some help.
(If you are curious about the company I showed you, It is just a site I found through Thomas Register, and there "main" page is
here. There is a telephone number you can call and get pricing information on the cable, splices (if needed), mounts, etc.)
About multiple pairs - you probably want them anyways, for any future expansion, paging, maybe a remote phone? Etc.
Karl P
Karl P