sflphone-client-kde: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/sflphone-client-kde - from package: sflphone-kde

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