EMarketer just released its mobile ad forecast for the US. I actually spoke to analyst Noah Elkin about the details of the forecast a few weeks ago. Vexing questions surround how to define the market and about the assumptions behind the growth figures and distribution of ad spend. The three main components of the spend in the eMarketer forecast are SMS, display and search (see graph below).
There's a whole category of "mobile marketing" spending that is potentially large and not reflected here because it's not "advertising" per se (inventory puchased in search, on sites or in apps), including app development and mobile optimization.
Here are the eMarketer numbers, which have been toned down a bit from prior estimates:
Compare the current online mix of ad spending in the US, where display (including video and rich media) constitutes about 31% of the online ad spend vs. search, which is closing in on 50% (46% at the end of 2008 per the IAB).