sipw: 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/lib/debug/usr/sbin/sipw - from package: libsipwitch1-dbg
/usr/sbin/sipw - from package: sipwitch

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

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