t38modem: 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/t38modem - from package: t38modem

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

Error in other languages:
t38modem: bevel nie gevind nie
t38modem: comandă negăsită
t38modem: comando não encontrado
t38modem: commande introuvable
t38modem: command not found
t38modem: käsku ei ole
t38modem: không tìm thấy lệnh
t38modem: komanda nerasta
t38modem: Kommando nicht gefunden.
t38modem: kommandot finns inte
t38modem: komut yok
t38modem: nie znaleziono polecenia
t38modem: níor aimsíodh an t-ordú
t38modem: no se encontró la orden
t38modem: no s'ha trobat l'ordre
t38modem: opdracht niet gevonden
t38modem: parancs nem található
t38modem: perintah tidak ditemukan
t38modem: príkaz nenájdený
t38modem: příkaz nenalezen
t38modem: команда не найдена
t38modem: командата не е открита
t38modem: 命令找不到
t38modem: コマンドが見つかりません