SQL Server 2012 now uses dynamic ports for each SQL instance which is subject to change. SQL client applications discover the which port the instance is now running on by querying UDP 1434, the SQL Browser Service which returns the correct port. My SQL Server instance is currently running on TCP25463 and the Browser Service tells the client to connect to this port.
This is similar to the way the RPC Endpoint Mapper works for RPC based Microsoft applications. In terms of network lockdown and ACL rules, the network engineers are usually unhappy about this approach as it means they need to keep the entire port range open.