Exchange 2013 has been in RTM status since today. So it won't be long before the new Exchange Server is available. Volume license holders with Software Assurance contracts will be able to access Exchange 2013 from December 1, 2012. Exchange 2013 will then be generally available from the 1st quarter of 2013.
Click here for the article on the Exchange Team Blog:
http://blogs.technet.com/b/exchange/archive/2012/10/11/the-new-exchange-reaches-rtm.aspx