Many analysts simply assume that mobile advertising will follow the well-worn path of PC advertising, only perhaps in a more accelerated fashion. Thus you get mobile advertising forecasts that show a relatively smooth progression of ad budgets into mobile, with search and display being the two main ad categories (calls fall into both). There's a longer post to be written about these assumptions and why they may not play out as expected -- especially with respect to location-based ads on mobile devices.
Overall there are relatively few mobile search impressions available outside of Google. So most of the ad inventory being sold today is some form of mobie display. However there's also something a "war on mobile display." That's really about the business model: CPM/CPC vs. CPA.
It's largely being waged by firms whose business models that are not CPM or CPC based. Companies that use a pay-per-[app]-install or other CPA models have attacked CPM or CPC-based mobile display with the idea of the "fat finger problem."
The argument is that a huge volume of mobile display clicks are simply mistaken or perhaps even fraudulent in some cases.
Source: Trademob (9/12); based on analysis of 6 million mobile ad clicks
There's also the idea, often discussed, that consumers don't like mobile display advertising and consider it to be just a notch above spam.
More recently Marchex, which has transformed itself into a call-based advertising platform and network, asserts that the overwhelming majority of mobile display impressions and clicks are nearly worthless. In a study, released in December, involving six major display ad networks Marchex found that it took almost half a million ads to generate one "quality" phone call:
We examined a set of mobile display ad campaigns across the six largest mobile display networks to investigate the real, measurable performance of these ads. The call to action on all advertisements was a phone call. Performance was based on the number of high-quality calls driven by the media investment. Marchex defines high-quality calls as those that do not include misdials and spam; existing customers looking for support services; and unproductive calls (e.g. too short).
Our advertisers included national, branded businesses in Education, Insurance, Home Services and Entertainment. We conducted the study on major mobile ad networks and employed media tactics ranging from highly targeted to broad buys. Ad spend was distributed across networks and advertisers to ensure statistically valid conversion results on the back end.
Marchex said that in its test it took 494K impressions to generate 2,481 clicks, which in turn generated only one "quality" phone call (as defined above). That single call effectively cost $302 according to the company, because of all the wasted impressions.
Source: Marchex (2012)
I exposed these findings to one mobile ad network, which disputed them and said on its network the ratio of impressions to qualified calls was much smaller: 15:1 rather than 494K:1.
The Marchex argument is that it's simply cheaper to buy calls directly than to buy mobile display impressions. The company's study needs to be replicated before we can conclude that Marchex's findings are valid across networks. There's also the argument about awareness vs. direct response -- most national advertisers currently are just seeking broad awareness and scale.
Regardless Marchex's findings and the other data above collectively fuel pervasive doubts about the value of mobile display advertising.