Squirrelmail contains a nice function in the sources to convert unicode to entities:

<?php
function charset_decode_utf_8 ($string) {
      /* Only do the slow convert if there are 8-bit characters */
    /* avoid using 0xA0 (\240) in ereg ranges. RH73 does not like that */
    if (! ereg("[\200-\237]", $string) and ! ereg("[\241-\377]", $string))
        return $string;

    // decode three byte unicode characters
    $string = preg_replace("/([\340-\357])([\200-\277])([\200-\277])/e",        \
    "'&#'.((ord('\\1')-224)*4096 + (ord('\\2')-128)*64 + (ord('\\3')-128)).';'",    \
    $string);

    // decode two byte unicode characters
    $string = preg_replace("/([\300-\337])([\200-\277])/e", \
    "'&#'.((ord('\\1')-192)*64+(ord('\\2')-128)).';'", \
    $string);

    return $string;
}
?>