There are no cooling off periods in the UK any more for phones bought from shops as u get a demo in store, How ever if you buy over the phone or on the internet you get a 7 day cooling off period. Go direct to Vodafone i got

750 any netowork mins
unlimited Data
unlimited text
unlimited voda to voda calls
unlimited landline calls
vodafone passport

For £30 a month including a Free phone :-D just haggle them they will move