Apple and Google are enemies and partners at the same time due to asymmetric competition. According to a report from Morgan Stanley, Google could pay more than $1 billion in 2014 to remain the default search engine on iOS. In 2009, Google paid only $82 million for the privilege. Analyst Scott Devitt believes that it is a per-device deal growing every year.
According to the report titled “The Next Google Is Google” and the table below, the total traffic acquisition cost is somewhat proportional to the number of iOS unit sales, with a traffic acquisition cost rate slowly going up from $3.2 per unit last year to an estimated $3.3 per unit this year and $3.5 per unit next year. That’s why the total traffic acquisition cost is going to increase in the coming years if iOS sales keep growing.