This is my css for epub font hack in Sony (and it's working)
Code:
@font-face { font-family: "Charis"; font-weight: normal; font-style: normal; src: url(res:///Data/fonts/CharisSILR.ttf);}
@font-face { font-family: "Charis"; font-weight: bold; font-style: normal; src: url(res:///Data/fonts/CharisSILB.ttf);}
@font-face { font-family: "Charis"; font-weight: normal; font-style: italic; src: url(res:///Data/fonts/CharisSILI.ttf);}
@font-face { font-family: "Charis"; font-weight: bold; font-style: italic; src: url(res:///Data/fonts/CharisSILBI.ttf);}
body { font-family: "Charis", serif; line-height: 1.25em; }
I think you miss Data directory before fonts, and fonts directory should be lower case