Art:
Chances are, they will terminate your T1 in an outdoor NID. This NID will provide you with an RJ48X jack. If you wire a straight-through cable using the 568A or B wiring plan (same at both ends of course), then you should be fine.
I assure you that the telco will not connect your new circuit to the other pairs in your existing building wiring. They will leave it outside at best. Regardless, that is bad practice anyway to loop a T1 circuit from outlet to outlet in a residence. Forget about using the existing wiring, seriously.
You really should install a home-run cable and terminate this cable on a true RJ48X jack at the equipment end to keep it proper.
Using existing pre-wiring in a new home wired by electricians is not worth even trying to use. You need to route the T1 circuit via a clean cable run to your channel bank or router.
Oh, and:
