LongWeek, all the information was on an 'opt in' basis. The vast majority of parents opted in.
Parents/guardians could allow any or all of their contact information to be used. ExH used to allow his mobile number to be published. I allowed my name, address, home phone and email address to be included. A friend had her name, number and her parents' name, address, and her dad's mobile phone number (he was the only GP of the child who spoke English) as her DD spent the majority of time outside school with her GPs thanks to the mum's work hours. A neighbour whose DH was an FBI agent gave a PO box as a postal address but gave an e-mail address for the mum. Nobody gave non-inclusion a second thought. Life is too short to wonder why X family only gave a phone number and child's name, or didn't give a phone number.
Before the local TV stations got together a really organised system to announce weather-related closures of schools with a ticker tape along the bottom of the screen (due to blizzards or extreme heat/poor air quality warnings), the school relied on a phone tree to inform parents of a closure decision, all based on the directory.
YY to police being well known as we have a community policing policy here, with a neighbourhood officer living in each policing area of my municipal area. Those police officers with children in my DCs' school were well known and often came to the school in uniform complete with weapon to pick up their children - one used to be a room parent and was able to get all sorts of great access to the local fire station for kindergarten days out - and all their info was in the directory.
YY also to the honour code - nobody uses the directory for business purposes. It happened once in my experience, but the parent was ratted on and the school had a word.
It is a great community promoter, much better than the white pages or leaving parents to forge their own little networks based on cliques at the school gates, or develop networks centered around scouts or sports (all team rosters were shared and included contact details too). It eliminates the party invitation problem from school life (the school only allowed invitations to be distributed for all-class parties). It means people know the names of parents even if a child stays in the extended day room after school or goes home with a nanny or CM or relative and can make contact for socialising or lifts for children. Parents in the US do a huge amount of carpooling to parties and sports practices and events even at a young age, and sleepovers are very common, at least in my area; this is facilitated by having contact details at your fingertips.
The directory also had the daily bell schedule and the annual calendar listing all events, which set in advance. Another feature in my DCs' school directory was driving directions to all the other schools in the sports conferences and some parking and school gym entrance and playing field location details, all of which came in very handy.
The really important part of the school directory was the inclusion of the contact details for the teachers, principal and school board members, along with the 24 hour response guarantee. Teachers did not stand at the school door fielding parents inquiries or trying to conduct private conversations in a sea of people. If you said you were available to take a call from a teacher after 6 pm (for example) then a teacher would call you after 6. Yes, all of that could have been sent out on a couple of sheets of paper without any family information, but including school contact info along with parent contact information expressed the ideal of everybody being equal and equally approachable.