A few truthes......
Lets dispell some myths and nip some rumours in the bud -
The femtocell connects to Vodafone using an IPSec tunnel so nobody will be able to intercept and listen in to your conversations over the femtocell. Also you configure it to accept connections from up to 32 numbers, any 4 of which can use the device at the same time. If someone isn't listed in your router they can't use it so nobody unauthorised will be chewing up any bandwidth.
You can't use it outside the UK as it registers the location, devices in the USA use GPS - quite how they are doing it in the UK I don't know but there will be some technical wizardry stopping it's use all over the world.
Lastly it's not meant to replace wi-fi, the frequency 3G runs at isn't the best at penetrating buildings......hence why it's been dreamed up. It's available as part of a contract so you don't have to shell out 160 notes for it, you can get one with your upgrade. Calls will be charged as you are still using the Vodafone core network and all the equipment like the authentication servers, SGSN's, Media Gateways, to name a few.
I guess I will come back and correct some more myths and misconceptions another time, it's too warm to do it now.
A battery back up won't be much use, if your power is out then your broadband router won't have any power either so no connection to the internet equals no femtocell.