Using DISM to enable features

From windows 2012, pkgmgr has been deprecated and cannot be used from the command line to install features on windows server.

Use the following instead to install a feature with a one line command:

dism /online /Enable-Feature /FeatureName:TelnetClient

Ive previously blogged about pkgmgr here –

Pkgmgr utility to install windows features including Telnet

Install Telnet Client by using a command line

On Windows 7, Windows Server 2008 R2, Windows Server 2008 or Windows Vista you can use the following command line procedure to install Telnet Client.

Open a command prompt window. Click Start, type cmd in the Start Search box, and then press ENTER.
Type the following command:

pkgmgr /iu:"TelnetClient"

If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Continue. When the command prompt appears again, the installation is complete.

Pkgmgr options:

Full list of windows server packages