I think you have to sign an initial 12 month contract - they are not going to install it without some sort of tie in.
The second bog cost £10/month on M and L but £5 on XL
I have 2 V+ boxes XL TV, 50Meg BB and basic telephone (free w/e and eve) and caller display (yes, annoyingly it is a paid for extra) and pay £68/month
The UK call centres (Glasgow?) are, in my experience, a lot better but I think it's just pot luck.
Make sure you find out the cost of equipment and connection charge as well, upgrades to 50Meg cost for a call out and connection but if you are having the whole lot done in one time it might be different, there is talk of upload speeds being increased sometime this year, they are trialling 5Meg but no news of when it will be rolled out.
Cable BB is faster than Sky - 20 Meg is 20 Meg and 50 Meg is 50 Meg in my experience.
Sky's CS is very good whereas Virgin's can be , how shall I put this, variable.
When there are no problems there is very little to chose between the two on TV and Telephone (you know Sky has more HD Channels but V+ you can record/watch more channels at a time) one thing Virgin don't make a lot of is the catchup TV and TV on demand which I was pleasantly surprised by. Virgin Internet speed is great.
Good luck and have fun
