Coexistence with Exchange 2013
If you are on Exchange 2010 you will need SP3 to coexist with Exchange 2013.
Exchange 2010 SP3 was released yesterday.
blogs.technet.com/b/exchange/archive/2013/02/12/released-exchange-server-2010-sp3.aspx
If you are still on Exchange 2007 you can install RU 10 and coexist with 2013. It was released yesterday as well.