gammu-detect: 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-detect - from package: gammu

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

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