PHP: Converting a byte array into a UTF-8 string

We've got some stupid and unrecompilable client code which sends a string to a webservice. The format of the string is created using this code in C#

        string strAscii = "";

        System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding ( );
        byte[] arrOrg = encoding.GetBytes ( strOrg );

        for ( int i = 0; i < arrOrg.Length; i++ )
        {
            strAscii += arrOrg[ i ].ToString ( "x2" );
        }

        return strAscii;

This has got to be unravelled by a PHP page. The only way I've managed to get this to work is by converting each couplet of the string to a byte value and putting them into an array.

And then by running this monstrosity:

$arrBytes = array( 0xc3, 0xa9); // this is a single UTF-8 character (e acute)

$fh = fopen("./temp.tmp", "w+");
for($i = 0; $i < count($arrBytes); $i++)
{
    fprintf($fh, "%c", $arrBytes[$i]);
}
fclose($fh);

$str = file_get_contents("./temp.tmp");

echo $str;

This works, but it's ridiculous.

Is there any better way of doing it? I've tried all the "standard" type ways, mb_convert_encoding, iconv and pack but to no avail.