0345 numbers are generally not free to call from O2. However, if you have spare free minutes in contract or bundle, they will be compatible with 0345 numbers so you can call them effectively without charge until your free minutes allowance expires. This is true for all O2 mobile phones and landline call packages in the UK.
What are 0345 numbers?
0345 numbers are standard-rate non-geographic numbers that exist to replace the more traditional business-rate 0845 numbers.
How much do 0345 numbers cost to call, and why are they so popular?
03 numbers, including 0300, 0330, 0333, 0343, 0344, 0345, 0370, 0371, 0372 and many more variations, cost the same amount to call as any geographic 01 and 02 number and are just as eligible for free minutes. Business-rate 08 numbers however, such as 0843, 0844, 0845, 0870, 0871 and 0872 numbers, are not compatible with free minutes allowances on mobile phone contracts and landline call plans, and generally cost a lot more to call than standard rate 01, 02 and 03 numbers, especially when calling from mobile phones. For this reason, in 2015 it became illegal for companies to use 0845 numbers and other business-rate numbers for after-sales customer service helplines, and the 0345 number range was brought in to replace 0845 numbers with matching equivalents that are charged at standard rate.