If you are behind a restrictive firewall that blocks you from being able to access the non-standard ports that cPanel, WHM, and webmail use, you can use the following URLS
This of course only works if those subdomains are pointed to the servers ip address. By default, they should if you are using the nameservers of the cpanel server.
FYI: the non-standard ports that cpanel, whm and webmail use on a cpanel based server are:
cPanel: 2082 and 2083
WHM: 2086 and 2087Webmail: 2095 and 2096