Communications: Voice, Radio and Data - Cat5 cables in my electrical closet...where do they go?

(this is my first foray into the intricacies of home wiring...please be gentle)

In my basement's electrical closet, there are 5 or 6 cat5 cables that just come out of the rafters and dangle there, they aren't crimped or connected to anything. There are also no data jacks anywhere in the home, and i've pulled off a few phone jack wall plates and I don't see anything interesting. (home is about 10 years old) I'm trying to determine if a wired home data network is possible so I'm trying to figure out...

1) Is there any way to tell where the cables go?
2) Are the cables there to support the phone cabling system or were they an attempt at creating a data network?
3) Why would a builder leave cables dangling like that?

Sorry I know this is a little vague but i'm not sure where to start.

Many thanks in advance.

A little more sleuthing than pulling a couple of wall jacks may help. Pull every wall jack that isn't an AC receptacle or wall switch, including some that may be blank covers. Look closely behind phone jacks -- the cable may be tucked inside.

If the cables were there to support the phone system they would most likely appear at the phone jacks. Is there another location where electrical wiring comes together in the house? Near the phone company's NID (network interface device)? Or maybe they go up to the attic and branch to the rooms from there?

A builder's electrician might leave cables unterminated for "future use", but there should be an as-built drawing somewhere that shows where they go. Have you called the builder?

Well, I had wires like that hanging in the coat closet downstairs at my last house, though it was more like 15 not 5-6. It was the pre-wiring for an alarm system. 1 wire for every downstairs window and door.