[comp.dcom.telecom] phone co. does zipcode/phone-prefix correlation?

cmoore@BRL.ARPA.UUCP (10/30/87)

Some phone books covering rural areas have a separate section for each phone
prefix, with an occasional case of 2 prefixes in the same territory.  Because
the phone prefix won't necessarily match the mailing address, it is necessary
to preface the white pages with a community list which says "for (community)
see (exchange place name)".  Some phone prefixes have place names which are
nonpostal names, and when you get out along the rural delivery routes you
may find your mail coming from one town and your phone line going to a town
in the opposite direction.

How much work goes into this?