The long awaited feature has been added to the PHP repository yesterday using the Dimitry Stogov’s implementation.
Define a namespace :

namespace Zend::DB;
class Connection
{
    //code
}
function connect()
{
    //code
}

You can import namespaces or class name like this:

require 'Zend/Db/Connection.php';
import Zend::DB;
import Zend::DB::Connection as DbConnection;
$x = new Zend::DB::Connection();
$y = new DB::connection();
$z = new DbConnection();
DB::connect();