How much does it cost to call an 0300 number on O2?

0300 numbers are charged at the same rate as 01 or 02 numbers when you have O2 as your service provider. They are also included in whatever amount of free minutes you are allowed on your chosen phone plan. This is a result of government legislation introduced in Spring 2007 which said that 03 numbers must be charged at the same rate as 01 or 02 numbers. After your free minutes are used up you will be charged at O2’s standard UK rate.
0300 numbers were introduced as an alternative to 08 numbers (such as 087) in 2007. The 0300 number range can only be used by Public services and other not for profit organisations. This was new stipulation was created following an uptick in demand for phone numbers by several large public bodies.