utf8_to_unicode in PHP

想使用8:UCS2格式编码下行短信的时候,需要把UTF8转换成Unicode的十六进制编码，但是PHP没有内置Unicode的支持，怎么办呢?

/* *
* 从UTF8转换成unicode beta1.0
* @param mixed $string要转换的字符串,
* @return unicode的十六进制编码
*/
function utf8_to_unicode_hex( $string ){
$length = strlen ( $string );
$outstring = "" ;
for ( $i = 0 ; $i $asc_value = ord ( $string [ $i ]);
if ( $asc_value > 127 ) {
if ( $asc_value >= 192 && $asc_value $str_dec = ( ord ( $string [ $i ]) & 0x3f ) $i ++ ;
$str_dec += ord ( $string [ $i ]) & 0x3f ;
$str_hex = dechex ( $str_dec );
$outstring .= str_pad ( $str_hex , 4 , " 0 " , STR_PAD_LEFT);
} elseif ( $asc_value >= 224 && $asc_value $str_dec = ( ord ( $string [ $i ]) & 0x1f ) $i ++ ;
$str_dec += ( ord ( $string [ $i ]) & 0x3f ) $i ++ ;
$str_dec += ord ( $string [ $i ]) & 0x3f ;
$outstring .= dechex ( $str_dec );
} elseif ( $asc_value >= 240 && $asc_value $str_dec = ( ord ( $string [ $i ]) & 0x0f ) $i ++ ;
$str_dec += ( ord ( $string [ $i ]) & 0x3f ) $i ++ ;
$str_dec += ( ord ( $string [ $i ]) & 0x3f ) $i ++ ;
$str_dec += ord ( $string [ $i ]) & 0x3f ;
$outstring .= dechex ( $str_dec );
} else {
$str_hex = dechex ( ord ( $string [ $i ]));
$outstring .= str_pad ( $str_hex , 4 , " 0 " , STR_PAD_LEFT);
}
} else {
$str_hex = dechex ( ord ( $string [ $i ]));
$outstring .= str_pad ( $str_hex , 4 , " 0 " , STR_PAD_LEFT);
}
}
return $outstring ;
}