Originally Posted by HarryT
But the typical user is highly unlikely to have a font with the appropriate characters in it. What I meant was that the only way to guarantee that the text will be readable by the end user is to embed the font in the document and (AFAIK) Mobi doesn't support font embedding, unlike PDF (and also the Sony Reader too).
epub supports font embedding, also. When the Sony has Digital Editions and when the Cybook supports epub, ancient Greek will be no problem.