Hi Chris,
I tried two different long cables (10 metres and 15 metres) plugging from the NBN connection box into the Technicolour modem in the lounge room, both cables did not allow me to get a WAN link light on. Tried on the replacement modem as well. However, when I ttested with the Netgear EVG2000 modem (from Telstra Smart Velocity), no issues at all.
Therefore, this particular modem seems to be weak picking up the WAN signal.
Rox