linphone: 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/linphone - from package: linphone

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

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