Never saw cat 5e in two pair. I have seen cat 5- 2 pair used for patch cords. I didn't think it was possible to maintain the cat 5e characteristics without the other two pair.
You can use it for 10/100 baseT ethernet as only two pairs are used but you will have problems trying to figure out how to terminate it.
Since you are only using this for voice it's no big deal and that's probably about all it's good for. If you are looking for cost effectiveness look at cat 3 for voice but I suspect somebody was trying to unload that stuff real cheap.
-Hal
