This really is nice and easy to do.
From memory, you just make a copy of smtp_psa that you'll find in /etc/xinet.d and call it something else, like smtp_2525
Now edit this new file. The firt line is the key. That defines the port. "service xxx"
Now the xxx by default is "smtp". But that's a descriptive word for the service not a port number.
The file that maps these service words to port numbers is /etc/services
port 2525 isn't defined in mine (RH9) but may be in yours. If it is then just use the appropriate service name. If it is not, try adding it, like this:
myspecialport 2525/tcp
myspecialport 2525/udp
(two lines, one for udp and one for tcp. Also note that there is a tab between the name and the number, not a set of spaces.
Then use "service myspecialport" as the first line in your smtp_2525 file.
When finished restart xinetd (service xinetd restart) and hopefully bob's your relative.
Remember to open port 2525 in your firewall if need be.
MAKE COPIES OF /etc/services and be prepared to delete your smtp_2525 files in case things go wrong. In fact back everything up. Use my advice at your peril. I'm not always right
Faris.