Now that you mention it, I looked that up and found the same thing.
Although I don't know which name came first, it's possible that

1.  They changed the spelling from Una-Fon to Unaphone because people
mispronounced it (some people still do);

2.  They changed it from Unaphone to Una-Fon to use as a trademark name.
For example, Leedy made and sold the "Vibraphone" and Deagan made and
sold the same type of instrument under the name "Vibraharp".

I don't know of any other variant spellings in the Deagan literature.

Danielle Squyres

 [ Thanks, Danielle.  -- Robbie