There are 4 distinct telephone wires entering my house. I assume they each feed a phone socket in different rooms.
this is standard installation. you have two copper cable pairs (=4 wires). only one pair is used, with one spare pair.
you therefore have one copper pair (local loop) back to your local exchange/switch.
i assume you are on carrier pre-select with esatb, as you say you still pay (eircom??) for line rental seperately.
your calls will be routed to your selected carrier by a catagory on the Line Interface in the eircom Exchange, which can be for any combination of Local, National or International calls. you will have selected your requirements with your carrier.
this happens automatically and you don't have to enter any codes, etc.
calls from various points from your house are carried on the same copper pair into the local exchange, and therefore will all be treated in exactly the same way.
that is, unless you are using a 5 digit over-ride code, which allows you to by-pass your carrier for that call only.
there is a pretty good explanation here: [broken link removed]
get back to me by PM if you want further info and i will endeavour to sort this out.