OT: Ethernet/Telephone cabling

[robertlaferla at comcast.net (Robert La Ferla)]

I purchased a new house that has each room pre-wired with CAT-5 jacks.  
All the cables meet in the basement but there are no connectors on 
them.  These same cables are also used for telephone.  Each cable has 8 
conductors (in 4 twisted pairs).  One twisted pair (or 2 conductors) is 
used for telephone leaving 6 conductors (3 twisted pairs) free.  My 
question is can I have both telephone and Ethernet on the same cable?  
If so, what speed?  Do I have other options like some sort of Ethernet 
telephone?

Thanks in advance,
Robert