You cannot phone 03456 numbers for free from an O2 device unless you have inclusive minutes remaining on your tariff, as these can be used to call all 03 helplines for no additional charges.
O2 call costs – 03456 numbers
If you do not have any inclusive minutes remaining on your O2 Pay as you Go rewards bundle or your Pay Monthly contract you will need to pay them an access charge plus a per-minute rate depending on how long the call to an 03456 number lasts. Therefore if you do not have the minimum amount required (70p for pay monthly customers, 60p for O2 Pay & Go users) you will not be able to make the call. However as stated above if you do have inclusive minutes remaining on your allowance you will be able to phone 03456 numbers for free.
Who uses 03456 numbers
03456 numbers are used by companies, non-profit organisations, government bodies and charities as helplines. They are hugely popular due to their easy-to-remember structure, therefore they attract high prices in telephone number auctions.