Just one example.
The Basic Ingredients of a Successful Mobile Advertising Campaign – The inneractive Blog
“According to many predictions, by 2015 mobile advertising in the U.S alone will surpass the $50 billion mark.”
5 Brilliant Mobile Marketing Campaigns – Mobile
Please note that what’s described above is much more complex and involves many more professions than just serving simple static ads via an ad network. Actually, it’s in line with what e.g. MM3 provides.