Telefónica is opening up phone usage and browsing data from its O2 customers to brands to allow them to target ads at London Underground users. Exterion Media has partnered with Telefónica to access anonymous data from 25m O2 customers to generate "actionable demographic and behavioural detail" about Tube users. O2’s data includes information on customers’ lifestyles, gender, age and affluence. The telecoms giant ascertains affluence based on how customers use their phones.