In the form of "hallow", its possible earliest ancestor, "hello" dates back to at least 1340 and was used by Chaucer. In its modern form, it was first recorded in 1883 and its popularity rose with the advent of the telephone: it was Thomas Edison’s idea to use "hello" as a greeting, a suggestion which won out over Alexander Graham Bell’s, "ahoy".
In France, the first telephone was installed in Paris in 1879, and the American form of greeting was used and then francised to become allô, but it looks like "hello" may be of French origin:
Alteration of earlier "hallo" (1840 in Dickens’ Barnaby Rudge), itself an alteration of "holla", "hollo", a shout to attract attention (1588), a natural native formation, used to attract attention of someone, perhaps from the earlier English exclamation "holla!" said to be borrowed from Middle French holà (ho, exclamation to attract attention + là, there); or perhaps influenced by German Hallo, holla, used to attract attention. The more probably explanation is that "hello", "hallo", "holla" and "hollo" are all natural formations in English and that they are parallel to natural formations in German, French and other, if not all, languages.
Chambers dictionary of etymology
Not everybody likes "hello": in 1997, Leonso Canales Jr. from Kingsville, Texas, proposed that Kleberg County should designate "heaven-o" as the county’s official greeting, on the grounds that "hello" contains the word "hell". His proposal was accepted unanimously even though, as shown above, "hello" is not etymologically related to "hell".