Have you found yourself on a server or workstation that doesn't have telnet (typical in new builds and new Azure VM's from the gallery), and need it to test port connectivity? Did you receive this error when you tried to execute telnet in cmdshell or powershell?

telnet : The term 'telnet' is not recognized as the name of a cmdlet, function, script file, or operable program.
Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:1

Three quick ways to add the Telnet Client to the server you're on right now that are much faster alternatives than adding telnet via the Windows features section of the Control Panel. Note that you must launch PowerShell or Command Prompt as an administrator to run these commands, so non-administrators will need to track down a helpful sysadmin first.

Install telnet via DISM (via cmd/PowerShell):