function encode_gsm($string){

$dict = array(
 '@' => "\\\\x00",
 '£' => "\\\\x01",
 '$' => "\\\\x02",
 '¥' => "\\\\x03",
 'è' => "\\\\x04",
 'é' => "\\\\x05",
 'ù' => "\\\\x06",

//NON FONCTIONNEL
 'ì' => "\\\\x07",
 'ò' => "\\\\x08",
 'Ç' => "\\\\x09",

 'Ø' => "\\\\x0B",
 'ø' => "\\\\x0C",
 'Å' => "\\\\x0E",
 'å' => "\\\\x0F",

//NON FONCTIONNEL
 'Δ' => "\\\\x10",

 '_' => "\\\\x11",
 'Φ' => "\\\\x12",
 'Γ' => "\\\\x13",
 'Λ' => "\\\\x14",
 'Ω' => "\\\\x15",
 'Π' => "\\\\x16",
 'Ψ' => "\\\\x17",
 'Σ' => "\\\\x18",
 'Θ' => "\\\\x19",
 'Ξ' => "\\\\x1A",
 'Æ' => "\\\\x1C",
 'æ' => "\\\\x1D",
 'ß' => "\\\\x1E",
 'É' => "\\\\x1F",

 // all \\\\x2? removed
 // all \\\\x3? removed
 // all \\\\x4? removed
 'Ä' => "\\\\x5B",
 'Ö' => "\\\\x5C",
 'Ñ' => "\\\\x5D",
 'Ü' => "\\\\x5E",
 '§' => "\\\\x5F",

 '¿' => "\\\\x60",

 'ä' => "\\\\x7B",
 'ö' => "\\\\x7C",
 'ñ' => "\\\\x7D",
 'ü' => "\\\\x7E",
 'à' => "\\\\x7F",

 '^' => "\\\\x1B\\\\x14",
 '{' => "\\\\x1B\\\\x28",
 '}' => "\\\\x1B\\\\x29",
 '\\\\' => "\\\\x1B\\\\x2F",
 '[' => "\\\\x1B\\\\x3C",
 '~' => "\\\\x1B\\\\x3D",
 ']' => "\\\\x1B\\\\x3E",
 '|' => "\\\\x1B\\\\x40",
 '€' => "\\\\x1B\\\\x65"
);


$converted = strtr($string, $dict);

// Replace unconverted UTF-8 chars from codepages U+0080-U+07FF, U+0080-U+FFFF and U+010000-U+10FFFF with a single ?
    return preg_replace('/([\\xC0-\\xDF].)|([\\xE0-\\xEF]..)|([\\xF0-\\xFF]...)/m','?',$converted);
}