$ sudo apt-get update
$ sudo apt-get install isdnutils-xtools 

isdnutils-xtools is installed in your system.

Make ensure the isdnutils-xtools package were installed using the commands given below,

$ sudo dpkg-query -l | grep isdnutils-xtools *

You will get with isdnutils-xtools package name, version, architecture and description in a table

isdnutils-xtools package basic information: