Ping a port

Well, sometimes we need to know whether the port in open or block, we need to do some checking or troubleshoot through ping/telnet. We cannot ping a IP with port but we can telnet certain IP together with Port no.

For example:
Go to open command prompt, if we want to check whether port 21 is working for IP 203.166.87.9 what we need to do is
> telnet 203.166.87.9 21

please tell me it's work. thanks