linphonec: 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/linphonec - from package: linphone-nogtk

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

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