J.R.R. Tolkien (or rather his friend C.S. Lewis's brother Warren) has the answer!
Thank you very much for your suggestions about my telephone number, which I will consider. Removing the number from the directory seems better than the method adopted by Major W. H. Lewis in protecting his brother, which was to lift the receiver and say 'Oxford Sewage Disposal Unit' and go on repeating it until they went away.
-- Tolkien's Letters, Letter 287
