SELECT *
FROM messages
WHERE recipient_id=? AND status='NR'

##</code><code>##

UPDATE messages
SET status='OK'
WHERE message_id = ?

##</code><code>##

$msg = "original message"; # assume this is from the prev message

$reply = $newmsg . "\nOriginal Message\n------------\n" .
         $msg;

# and then just insert the reply into messages table with SQL insert

INSERT INTO messages (message_id, recipient_id, sender_id,
                      message, date, status)
VALUES (?, ?, ?, ?, ?, 'NR')