It's not random, you phone number is part of a NPA-NXX-XXXX. NPA is a number plan area (area code) which is known. NXX is N=2 to 9, X=0 to 9, is an office cod

It's not random, you phone number is part of a NPA-NXX-XXXX. NPA is a number plan area (area code) which is known. NXX is N=2 to 9, X=0 to 9, is an office code. XXXX is a station code, where X is 0 to 9.