I don't own a freebox anymore, so I am not able to maintain this script anymore... Please consider vadz work instead (https://github.com/vadz/Munin-Plugin-Freebox)
Hope this can be of any help.
See this inside doc for details and usage.
I wrote this quick and dirty plugin for munin to demonstrate a hardware failure to my ISP.
With this, you will be able to monitor the temperatures, the fan, the line SNR, ... of the freebox v6.
With this, you will be able to monitor the line SNR, various counters (FEC, HEC, CRC), rates of differents lines (WiFi, Ethernet, USB, Switch)... and even the status of the phone.