Well, I've booked the installation and it's on 5 April. I've said I'll keep the second box in the same place and the total bill is only £11.25 more than before although I'm not sure if that includes caller ID otherwise it will be £13 more.
The CS guy said that I can cancel the second box when I want, despite me quoting from the VM website that it has to be retained for 12 months but we'll see.
4 weeks
. Well, on the positive side, maybe some of the software niggles will have been resolved by then and I will always have the second box, I suppose!!