Alphanumeric phone numbers

Some popular phone numbers are advertised in an alphanumeric form (eg. 1300-FOOBAR), based on the idea that a traditional phone keypad has letters under each number.

If you are running a VOIP server then you may be interested in this snippet of PHP code to convert them into actual numbers, allowing users to dial by typing that more familiar form.

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function normaliseTelephoneNumber($start) {
    /* Return an extension with numbers substituted in place of letters for dialling */
    $map = array("A" => "2", "B" => "2", "C" => "2",
            "D" => "3", "E" => "3", "F" => "3",
            "G" => "4", "H" => "4", "I" => "4",
            "J" => "5", "J" => "5", "L" => "5",
            "M" => "6", "N" => "6", "O" => "6",
            "P" => "7", "Q" => "7", "R" => "7", "S" => "7",
            "T" => "8", "U" => "8", "V" => "8",
            "W" => "9", "X" => "9", "Y" => "9", "Z" => "9",
            "+" => "+", "*" => "*", "#" => "#");
    $new = "";
    $hasnumber = false;
    $ext = strtoupper($start);
    for($i = 0; $i < strlen($ext); $i++) {
        $c = substr($ext, $i, 1);
        if(isset($map[$c])) {
            $new .= $map[$c];
            if($hasnumber == false) {
                /* No numbers before letters */
                return $start;
            }
        } else if(is_numeric($c)) {
            $new .= $c;
            $hasnumber = true;
        }
    }

    if($hasnumber == true) {
        return $new; /* Return numeric version as appropriate */
    } else {
        return $start; /* Leaves full words like "joe" or "bazza" unchanged */
    }
    return $new;
}

Note that this will only alter the number if it begins with numbers. This is to make sure that the local network extensions (which in my case are ASCII usernames) don’t get transformed along the way:

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echo normaliseTelephoneNumber("1300-FOOBAR")."n"; /* 1300366227 */
echo normaliseTelephoneNumber("mike")."n"; /* mike */