A new report from eMarketer estimates that advertisers will pony up nearly $1.23 billion on U.S. mobile advertising by the end of the year. That's up nearly 75% from 2010. The fastest growing category was video, but it still only represents 4.7% of the market. Messaging-based advertising represents the largest piece of the pie at 36.1 percent of all mobile ad spending.
The report also projects the mobile advertising market will reach approximately $4.4 billion by 2015. This includes banners, rich media, video, search, and message-based advertising, and includes ads served on mobile phones and tablet devices.
Here's a pie chart provided by eMarketer that details the U.S. ad spending share by format.