Hi Mark,
Without exception as far as I know, all new boxes from Sky themselves need to be connected to the phone line for the first 12 months. After that, they don't. If you mean taking your brother's 6 month old box, it will be better than taking the new multiroom one because it gives Sky less time to catch you out. Sky+ is a good idea here anyway, as you won't be getting all channels so you can record quite a few for the "library" - i.e. record some programmes that are on when you are out or asleep for when there is nothing on worth watching.
I had a multiroom box as my first one out here - the new one delivered, not the original one. It took Sky around 5 months to realise it wasn't connected to a phone line. At this time, they contacted the friend who gave the multiroom box saying they should connect it to the phone line, or it would be billed from that point forward at normal monthly subscription rates for a single box, not just £10 a month as a multiroom 2nd box. So I ended up paying £10 to my friend for the first 5 months, and £41 per month from then on.
That all sounded a bit complicated, let me know if it wasn't totally clear!