gsmctl: 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/gsmctl - from package: gsm-utils

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

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