poff.wvdial: 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 Debian possible default full paths are:

/usr/bin/poff.wvdial - from package: wvdial

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

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