iaxmodem: 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/iaxmodem - from package: iaxmodem

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

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