I put this in my epubs:
Code:
font-face {
font-family: "Name of the Font";
font-weight: normal;
font-style: normal;
src: url(../Fonts/name_of_the_font.ttf);
}
and it'll works well, both in kobo and non-kobo devices.
This manner sigil would validate your epub and you'll be sure that you can read it correctly in every ereader you want.
HTH
HP