So currently At&t will charge you $325 if you cancel you contract after 30 days however if I read correctly, you can cancel you contact before the 30 days and not get charged at all? But of course you would still need to pay for that month off service..
You can check this out by clicking 'terms of service' http://www.wireless.att.com/learn/articles-resources/wireless-terms.jsp
You can check this out by clicking 'terms of service' http://www.wireless.att.com/learn/articles-resources/wireless-terms.jsp