[Don't know the proper English term for this-- you know, something like a company's private internal installation where you have to dial a 0 or 9 to get a line to the outside.]
Any embedded alphabetic string may be used to hide site-dependent information like area codes. Any such string is translated to a dialcode using the dialcode file. Suppose you have the following dialcode file:
With these translations, you can use a phone number such as Bogoham7732 in the sys file, which makes things probably a little more legible.