The X.25 routing command is a prerequisite for using X.25 or XOT with ODEX. This command needs to be entered in "configuration mode". If the Cisco prompt does not contain the word "config" then the router is not in configuration mode.
e.g.
MYROUTER# - normal mode
MYROUTER(config)# - configuration mode
Enter the command "configure terminal" to enter configuration mode.
If the command is still not accepted, then the router may not support this functionality, resulting in an error like the example below:
MYROUTER(config)#X25 routing
^
%Invalid input detected at '^' marker.
A minimum requirement is the IP PLUS feature set (some Cisco 805 routers are provided with just the IP feature set). Cisco can confirm the feature set of the router if provided with the output of the "show version" command.
XOT is only supported in IOS version 12.1(2)T and above (this can be checked by running the "show version" command (outside of configuration mode).