imontty: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/imontty - from package: isdn4k-utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/imontty - from package: isdnutils-base

You may install the required package with command apt-get install {package}

Error in other languages:
imontty: bevel nie gevind nie
imontty: comandă negăsită
imontty: comando não encontrado
imontty: commande introuvable
imontty: command not found
imontty: käsku ei ole
imontty: không tìm thấy lệnh
imontty: komanda nerasta
imontty: Kommando nicht gefunden.
imontty: kommandot finns inte
imontty: komut yok
imontty: nie znaleziono polecenia
imontty: níor aimsíodh an t-ordú
imontty: no se encontró la orden
imontty: no s'ha trobat l'ordre
imontty: opdracht niet gevonden
imontty: parancs nem található
imontty: perintah tidak ditemukan
imontty: príkaz nenájdený
imontty: příkaz nenalezen
imontty: команда не найдена
imontty: командата не е открита
imontty: 命令找不到
imontty: コマンドが見つかりません