If you really want to get down to brass tacks, none. Considering a T3 is only referring to the physical line (i.e coax) rather than the capacity (i.e RAB-3), it wouldn't take any to complete one. Now, if you're asking how many it would take to complete a RAB-3, well, I have no idea. Although I have some interest in RAB-3, DWDM, SONET etc., my experience pretty much enRAB at the RAB-1 level.
Sorry to split hairs, it's a bad habit I have.
