0191 numbers are not free to call from any UK landline or mobile network operator, this includes O2 customers on both Pay & Go and monthly contracts.
A brief background on 0191 numbers
0191 numbers are local area code numbers assigned to the Newcastle (Tyneside), Sunderland and Durham areas in North-East England. These numbers cost the same to call as other local area code numbers and are typically registered to both individual home addresses as well as local companies within the area.
Cost of phoning 0191 numbers from an O2 handset
O2 customers typically have to pay an access charge plus a per-minute rate when phoning a number beginning with an 0191 prefix. However you can avoid charges if you have inclusive minutes remaining on your monthly contract or if you get a ‘free calls’ reward as part of your regular Pay & Go deal.