The mobile economy – which includes 5G, the Internet of Things, smart cities and connected cars – is expected to account for 4.5% of North America’s GDP by 2020, according to mobile operators trade group GSMA . That’s a trillion value. But while people and businesses increasingly spend more time on mobile devices and technology, advertisers haven’t quite caught up, said Anindya Ghose, professor of information, operation and management sciences as well as marketing at New York University, who recently penned a new book, Tap: Unlocking the Mobile Economy. Ghose and Wharton marketing professor David Bell discuss the opportunities and pitfalls of mobile marketing on the Knowledge at Wharton Show on Sirius XM channel 111 . An edited transcript of the conversation follows. Knowledge at Wharton : As important as smartphones and mobile are to the U.S. economy, I’m a little surprised we’re not already at $1 trillion on our own right now.…