Ramiro,
The changes only need to be made on non-Internet connected Exchange servers. I’d like to note though that even though the timeout issue that this solution resolves is most often seen with non-Internet connected Exchange Servers, there have been reports of this problem occurring on Exchange servers which are connected to the Internet; this is attributed to network latency.
This method is the best practice that we're recommending.
I’d like to take this opportunity to point out Guillaume Bordier’s TechNet blog in which he has created a script to automate the .config file change. His script has not been tested by the Exchange Team, but you can read his post, and get the script at http://blogs.technet.com/gbordier/archive/2008/07/11/exchange-server-2007-rollups-nighmares.aspx.