Hi!
I've got 1 line and 2 phones on it (one in my room and one in living room). The only problem is that these rooms are on different floors and I don't hear when my parents tell me something. The question is: can I call to the other telephone in this situation ? (and it would be lovely if I didn't pay for it ;> ).
Nope.
It depends but it would be costly
You could always install a key system. Then you run the phone line from the telecomm into the key system, from there you assign each phone a phone id then you can use them as an intercomm.
Of course it'll cost a couple hundred for the key system and another couple hundred for each phone
