The phone book has never given me a direct "hit", i.e. a living relative, but has led to numerous serendipitous discoveries. For example, someone might tell me that "....their daughter married and lived a couple of houses away from the Hehirs in Coolbane......". So I look up the phone directory entries for Hehirs in Coolbane, discover that there are three of them, pick one at random, call the number, apologise for calling them out of the blue, ask if they have a few minutes for some questions, and (if they have time), I fire away. Some might consider this cold-calling a damn cheek but in no case has anyone shown the slightest sign of objecting or irritation and many in rural areas - particularly the elderly - will happily spend ages telling me about the genealogy of the locality. Not one such phone call has failed to "mine" interesting information and several have given me leads which have allowed me to find relations or neighbouring families or fascinating nuggets of the local history or culture in which my ancestors lived. The people I call go down on a list of people to call on next time I'm in the locality so as to get the info face-to-face.
Another random phone call was taken by a young farmer who said he hadn't a clue about the family I was looking for but I should speak to Mrs. XY, an elderly lady who knew all the local goings-on. Sure enough, the lady was a mine of information so I dropped in on her and she happily took me round the townland, showed me the ruins of two houses where Casey families had lived, explained to me that there had been three different Casey families in that townland, gave me names which allowed me to identify them in the 1901 census and made sense of other fragments of information I had collected.
When trawling the phonebook in the context of family history research it is important to be aware of the geography. Thus a person who lives in townland A may be listed under the adjacent townland B or under the name of a nearby small town or under the name of a village which includes that townland. So if you've been told that the person you are looking for lives in X in County Y and you don't find them there in the Eircom phone book, don't despair. Just open up your Ordnance Survey Discovery map of the area* and start entering the names of adjacent townlands, villages, towns and counties.
You might just find that the phone book leads you to that breakthrough. And if it doesn't, well , you'll get to know a lot of very interesting people on the way, thus underlining the Zen principle that the journey is important, not the destination. ('
* P.S. A much richer source is now the Clare County Library collection of online maps at http://www.clarelibrary.ie/eolas/coclare/maps/index.htm