Yes, there is. You need a program called lsof (ftp://vic.cc.purdue.edu/pub/tools/unix/lsof/) . To kill a telnet session you need the PID of its telnetd process. And to obtain this PID, you could use lsof this way:
lsof -i | grep <port_number>
It would return one or more lines, containing the PID.
Perhaps you could kill the session more cleanly if you do a ps -ef | grep <PID_of_telnetd> to know the PID of the child process of telnetd (probably a shell), and kill it instead.