This is a simple question to answer. A note about 0800 numbers first. They were marketed to business users and to the general public as being freephone numbers, their purpose being mainly as short term business lines but also used by the big players in creating helplines for instance. However they used to require payment on all mobile networks, including 02.
However this all changed as late as July 2015 where 0800 numbers became free whether you were calling from a landline or a mobile phone. For some reason, maybe due to the lack of marketing on the subject, 1 in 10 people are under the dubious impression you still have to pay for such calls.
So the answer to the question: “How much does it cost to call an 0800 number?” can now be answered as “Nothing”. It even says as much on the O2 website, so it should be beyond all doubt.
|Number starts with||Description||Cost from landlines per minute (approximate)||Cost from mobiles per minute (approximate)|
|0800 number||Freephone service||Free||Free|