gammu: 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/gammu - from package: gammu

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

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