ALEXANDER GRAHAM BELL invented the telephone. But Thomas Alva Edison coined the greeting.

The word "hello," it appears, came straight from the fertile brain of the wizard of Menlo Park, N.J., who concocted the sonorous syllables to resolve one of the first crises of techno-etiquette: What do you say to start a telephone conversation?

Two contemporaries of Edison credited him with the word, but too vaguely for Allen Koenigsberg, a classics professor at Brooklyn College who has a passion for early phonographs and their history. Resolved to sort out the "hello" mystery, Mr. Koenigsberg embarked on a tortuous search five years ago that led him, finally and triumphantly, to the American Telephone and Telegraph Company Archives in lower Manhattan, where he found an unpublished letter by Edison. Dated Aug. 15, 1877, it is addressed to one T.B.A. David, president of the Central District and Printing Telegraph Company in Pittsburgh. Mr. David was preparing to introduce the telephone to that city.

At the time, Edison envisioned the telephone as a business device only, with a permanently open line to parties at either end. This setup raised a problem: How would anyone know that the other party wanted to speak? Edison addressed the issue as follows: Friend David, I don't think we shall need a call bell as Hello! can be heard 10 to 20 feet away. What do you think? EDISON

It was a word of destiny. Over at the laboratories of Edison's rival, Bell was insisting on "Ahoy!" as the correct way to answer the telephone. It was trounced by "hello," which became the standard as the first telephone exchanges, equipped by Edison, were set up across the United States and operating manuals adopted the word. The first public exchange, opened in New Haven on Jan. 28, 1878, wavered between "hello" and the fusty "What is wanted?" in its manual. By 1880, "hello" had won out.