Identifying which Cat 5 cable goes to which port

I just bought a new house, and I was told that every telephone port is connected with a cat 5 cable, which routes to a central location in the basement. Apparently phone cables can also use cat 5 cables, but instead of using all 8 wires in the cat 5 cable, they use 4.

I have only one room that has an ethernet port in the wall, but I also want to convert the other rooms' phone ports into an ethernet port.

I was able to convert the ports in the walls by buying a new plate and the ethernet port insert, and 'terminating' all 8 wires into that insert.

The issue now is that since this used to be a phone port, the other end of the cable is still connected to the other phone cables in the basement, and have the same colored wires twisted together with this.
http://images.oreillyauto.com/parts/img/large/bwd/stp201x_1.jpg

The wires then, are most likely routed out of the house into the phone lines.

I need to identify which of the cat 5 cable goes to which phone port in the house so that I can attach the ethernet cable head.
http://www.myonetwothree.com/items/...0065_02_RJ45Adpt/PcAs_0065_02_RJ45Adpt_01.jpg

Because the cable is missing the head, it also makes it hard to test which cable goes to which room.
If there was an ethernet head, I could just connect a router and check the activity lights, but since there isn't I don't know the best way to check...

Any ideas?

 

you need a line tester.. not an easy job unless you have one..

 

I bought a line tracer from home depot for around $40, worked fine.