How can I determine if CAT5 cable is wired for data or phone?
If they are not terminated, they have no signals at all, until you terminate them and connect them to something. 

Blue/white(with blue stripe) is normally the "line 1" pair in cat 5 cable used for phones. Green/white(with green stripe) is the standard line 2 pair, in the presently unusual case that you actually have 2 land-lines. Pins 4&amp;5 for blue, 3&amp;6 for green, on an 8-pin RJ-45. I would open the box (or the "Customer side" of the box if it's a Telco disconnect, not as likely inside the house - normally inside the house wiring is all yours) and look.

If you have a meter, it's easy (if tedious) to sort out the unconnected ones, if you are saying that you have a utility room that has a bunch that not terminated there either - strip a little and connect a 9V battery to a wire pair, then go looking for the other end with 9V across the wires you put it on. Label as you go, and it will get faster as you'll have fewer to check. Test leads with clips make this process easier but are not absolutely required.

Use reasonable care when testing for live phone lines - if it happens to ring, the voltage is significantly higher than the 48V you see when the phones are on the hook. On the other hand if it's completely dead (not as common with E911 laws) there may be no voltage at all.