Alexander Graham Bell initially suggested that the standard greeting when answering a telephone should be 'ahoy', but instead 'hello' (suggested by Thomas Edison) was adopted.
This sentence cites two sources, a page on todayifoundout.com and the Wiktionary entry for ahoy. Both of these do not, however, provide further citations regarding Bell and ahoy.
Thomas Edison's connection with hello, which is of course the standard greeting these days, is fairly well established. (Incidentally, the OED entry for hello (behind a paywall) also says “[Edison's] rival, Alexander Graham Bell, preferred ahoy to be used”.) Another part of the claim is that hello ousted ahoy, and that Edison chose hello (partially) because it was different from ahoy—I'm not as interested in this as I am in whether Bell explicitly suggested that “Ahoy!” be the standard greeting.
I've found a book containing a report, said to be quoted from Thomas A. Watson, of the first long-distance telephone conversation in 1876, which states that Bell's first words were “Ahoy, Watson, Ahoy! What's the matter?”. However, Bell merely saying “Ahoy!” does not mean that he publicly endorsed or promoted it as a greeting instead of any other phrase.