It's been more than six months and they are still getting away with it. I didn't realise that the programme is sponsored by a rival pizza company on Sky One, Dominos and also gives out an 0871 number with no pricing information.
Pizza Hut have this graphic on their homepage:
How it's free I don't know!
And before you ask, the asterisk is "Not valid at Dine-in only locations", so no, they haven't found it upon their conscience to tell their customers what it will cost them to phone up.