The first 2 numbers in a circuit number are usually part of the LATA (local access and transport area) I am in Verizon area in LATA 246 and all Special Circuits start with 46XXXX. The next 4 characters after the LATA number are USOC code for the type of circuit. If the code starts with X this designates that it is a digital circuit. The last 6 numbers are the actual circuit number in the database of the local exchange or interexchange carrier.