The BT FON app should have a sort of "power save mode" for the FON WiFi just like the homehub has, and this is why.
When my home wifi shuts off at night, the BT FON app on my phone decides to log me into my neighbours FON accesspoint and chews through my FON minutes! Yeah I can get a 3rd party app to shutoff my WiFi, but it would be nicer if you could tell the FON app to not log you in between certain hours.