National non-geographic 03 phone numbers are not free to call on Vodafone or any other network operator unless your tariff contains inclusive minutes.
03 telephone numbers are used throughout the UK as customer service helplines for private companies, charities and government bodies. Normally you will have to pay a per-minute rate plus an access charge to Vodafone in able to call these numbers, generally these are most expensive for monthly mobile contract users compared to landline customers. However Vodafone customers on any tariff can call 03 telephone numbers for free if they get inclusive minutes or weekend call bundles on their deal.