Using telnet, you can make an educated guess whether a port on a remote host is open, closed or blocked by a firewall by the error message it throws.
If you get no error message, the port is open.
If you get an error like the following:
Unable to connect to remote host: No route to host
you are almost certainly seeing a blocked (by firewall or whatever) port.
If you get an error like the following:
Unable to connect to remote host: Connection timed out
the port is almost certainly a closed port.