They won't give up your spot. They will keep calling you until you pick up. They may also leave a voicemail or e-mail you asking for you to call back. They won't go down their lists until they have received a firm rejection of an offer.
True, but I think in this process, and especially during this time it might be nice to be kind. As someone on the firm side, it is usually a coordinator or administrative assistant who sends those e-mails on the student director's behalf. Not really good form by talking shit about firms before you even embark on your interview process IMO.