Mobile advertising is set to take off in a major way over the coming months, and by year’s end it will be the No. 3 form of advertising, surpassing print, radio and out of home. That’s pretty impressive for a format that did not even exist a few years ago. That prediction comes from eMarketer, the online advertising tracking firm, which predicts that mobile ad spending in the U.S. will shoot up by 83% this year, to $17.73 billion.