Since Windows Vista Telenet client is not coming preinstalled with newer OS’s including Windows 8. Probably the reason is the security as these communications are unencrypted and sniffers can intercept the information on the network.
If you still need to use Telenet you can do it very easily by just executing one command at command prompt. Open command prompt in Administrator mode and execute below command :
pkgmgr.exe / iu:"TelnetClient"
You won’t get any notification after the command execution completes but that is also and indication of successful command execution though it shouldn't.