The only known copy of the world's first telephone directory has surfaced in Connecticut, and has been put on auction.
The 20-page book containing the names and number of 391 subscribers around New Haven, Connecticut, was issued in 1878 - just two years after the invention of the telephone by Edinburgh-born Alexander Graham Bell.
The directory, on offer at Christie's in New York on June 17, will be auctioned along with a collection of noteworthy books and documents covering technology, science, math and philosophy over six centuries.
The phone book contains some useful advice for inexperienced callers.
"Should you wish to speak to another subscriber you should commence the conversation by saying, 'Hulloa!'" Discovery News quoted the book, as stating.
Tom Lecky, who is head of books and manuscripts at Christie's auction house, said: "The directions start off by amusingly saying, 'Never take the telephone off the hook unless you wish to use it...When you are done talking say, 'That is all,' and the person spoken to should say, 'O.K.'"
The book goes on to tell readers they should leave the 'lower lip and jaw free.'
