According to J.P. Morgan's 2010 Internet Industry Outlook, mobile advertising is expected to grow by 45% in 2010 to $3.8 billion fueled primarily by mobile message advertising (SMS Text):
Although still a small piece of $159.2 billion that is expected to be spent on direct marketing in 2010, mobile advertising is a fast growing segment. Other gainers include display ads rebounding to +10.5% and search +13.7%.
(sources: TechCrunch, MediaPost)