You can phone 0300 numbers for free on Vodafone only if you have inclusive minutes on your tariff, otherwise you will pay a two-part fee to make these calls.
Although 0300 numbers are not technically free to call on Vodafone you will be able to call them for no charge if you get the use of inclusive minutes on your monthly mobile contract or pay as you go bundle. Landline customers will also be able to call 0300 numbers for free during the stipulated period for their evening & weekend calls bundle. If you have run out of your free minutes you will need enough funds in your account to pay an access charge as well as a per-minute fee which will ultimately depend on how long the call lasts.