If you are in the UK, the UK phone system only uses two wires.
Second you are not allowed to touch anything upstream, of the Master Socket as that is the BT 'Demarcation Point'. If you do so and screw things up, expect a big bill from BT to put it right. (You mentioned the wires coming into the house - messing with them is a no no.)
The correct way to wire extensions is to take one wire of a pair from Connector 2 on the back of the faceplate of the Master Socket to Connector 2 of the first Extension Socket. Then do the same with the second wire of the pair from connector 5 on the Master to connector 5 on the first Extension. Now to the same from the first extension socket to tht second extension socket. This is the correct way to wire extensions and is called 'daisy chaining'.
Finally if you screw this up and cause damage to BT's equipment they are entitled to bill you for that as well. In other words if you do not know what you are doing it is best to leave it alone.
T
July 2009