Weren't supermarkets pulled up for that recently?
Buying in bulk sounds cheaper, but often not.
If they make the more expensive one look cheaper than the other, they can get hauled through the coals.
Orange has introduced new mobile broadband roaming prices that penalise bulk-buying. Take the rates for Europe. Choose to pay £3 a day and you'll get 30MB to use up by midnight each day. That's 10p a megabyte. Use it for 30 days and you'll pay £90 in all and get 900MB of data. Pick the 30-day bundles, available for £15, £50 …