Yes either his ISP or router is blocking the port, the ISP deny any port blocking so who knows what the issue is, anyway thanks for confirming the KB article, I had already seen that, just wanted to be sure, the file you mentioned httpsd.conf has the following remarks in the header:
# DO NOT EDIT THIS FILE!
# The contents of this file will be overwritten next time you upgrade Plesk
# or apply a patch to it, so any changes you make to this file will be lost.
#
# If you need custom changes, you should modify the
# file /usr/local/psa/admin/conf/httpsd.custom.include
So I guess I will need to update httpsd.custom.include too so that the next update to plesk changes are not lost
Any suggestions to an allowed port I was going for 23 yet in the KB reference "Please note that none of the ports (21, 22, 23, 25, 53, 80, 110, 443, etc...) used for the standard web hosting services (Apache, POP, SMTP, mySQL, proFTPd, BIND) can be used." other articles I read suggested changing to port 23 (Telnet) as that port should be unblocked, now I'm in 2 minds.