Different applications open different TCP ports for their use. To ask if one is secure or not depends on the app. If the BackOrifice trojan is listening on port 2038, no that's not secure. If the SSH daemon is listening on port 2038 then yes, that's pretty secure.
There are some standards - IE, http listens on port 80, https on 443, FTP on port 21, SMTP on 25, etc. The security of these apps depends on what server is being used? IIS on port 80? Not really very secure? Apache? Much better.
In short, it depends on the app that's listening, not the specific port.
- G