Numbers beginning 01, 02 and 03 are included in goodybag minutes. If you have no goodybag minutes available you will be charged 10p per minute from credit.
Guess its below -
Corporate numbers 20p per minute
Not sure where you got that from, but 03 numbers are included in goodybag minutes on giffgaff and are 10p per minute if you don't have a goodybag or have used all your minutes.