Most likely CAT 4 cable - only has 4 cores. You'll still be able to get 100Mbs on it...but CAT5e (or 6 if you really want) would be the way to go for new installations.
a CAT5 cable only uses 4 pins (1,2,3,6) so you can use the telephone cable if you want but I really dont recommend it because the cable is to thin so the longer the cable the more problems you face. Rather use solid core CAT5 cable for your infrastructure and then use the stranded CAT5 cable for the flyleads.