Is there a Linux functionality for remote control of Telnet/SSH logins?

I have users who log in using Telnet or SSH. If they have a problem or technical support question, I would like to be able to log in to the server with Telnet or SSH and type in a command that would show me everyone currently logged in, then let me take over any one of the logged in sessions. Once I am finished, I would disconnect. I haven't been able to find this functionality anywhere in Linux.

I know you have issues with it, but personally, I would use VNC! VNC stands for Virtual Network Computing. The system is a remote display system which lets one view a computing "desktop" environment, but from anywhere on the Internet and from many different varieties of machine architectures.

If you change your mind, here's a great article by Jeff Vincent for more specifics:
http://www.sourcecodecorner.com/articles/vnc/linux.asp