There are several methods of interconnecting network systems in order to use their resurces. There is vnc, remote desktop, secure shell, remote shell, telnet amongst others.
       Amongst these connection methods, telnet along with the rtools are the most considered insecure due to the fact that they handle all transactions in the clear, i.e, all information is passed in clear text, which increases the likelihood of them being eavesdropped.

On the other hand, if you find yourself in a windows environment, which we are all bound to, one time or the other, the only text based option for non-gui connections is telnet.
Before proceeding, I'll have to state that I don't encourage the use of telnet across the internet or other forms of public networks. You should only do this if you've set a vpn in place.

Telnet is supported by most major systems, Windows, MacOS Linux, UNIX, BeOS amongst others.
I particularly find it useful to use telnet with windows since one cannot secure shell into a typical windows box.
With earlier versions of windows, its pretty easy,
Windows 98, WinME, Windows XP come preinstalled with telnet and up to WinXP SP1 have telnet enabled.
Unfortunately with newer versions of Windows, you may need to play with the configs to get it to work.
Beginning with windows XP SP2, Vista and Windows 7. The telnet server seems to be disabled.
Even after enabling them there seems to be a problem,

-------------------------------
c:\>telnet winserver.radiodrive

Access Denied: Specified user is not a member of the TelnetClient group.
Server administrator must add this user to the above group

Telnet has closed the connection
Connection to host lost
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This occurs because Windows Xp by default force all incoming network connections, to a guest level of access.
This especially true of those connecting through an MSDOS command prompt. User connecting through a thirs party client may not face this same issue.

To work around this behavior, change the default behavior to enable the
local administrator and the members of the TelnetClients group to
connect to the network with their proper identities, not as guests:

1. In Control Panel, double-click Administrative Tools.
2. Click Local Security Policy.
3. Locate the policy in the "Security Settings\Local Policies\Security
   Options\Network Access: Sharing and security model for local accounts"
   folder.
4. Right-click the policy, and then click Properties.
5. In the box, click Classic - local users authenticate as themselves.
6. Click OK.

To enable the Telnet Client and Server in Vista and Win7,
- Go to the Control panel
- Choose  Programs
- Under Programs, Select Turn Windows features on or off
- Enable the Telnet Client and Server.