Mobile:$3.4 billion last year, 9 percent of web dollars

This isn’t a particularly surprising revelation but it’s significant nonetheless: Mobile advertising is growing at an astonishing rate, underscoring a greater paradigm shift in internet usage from desktop to hand-held.

Half of all U.S. cell phone users have smartphones, nearly a third of Americans own tablets, and an increasing number of them rely on mobile as the only way to access the web.

More and more advertisers are trying to connect with these people, whom they could once reach via their desktops, via their mobiles, and it’s led to huge increases in mobile advertising.

Spending on the category spiked by 111 percent in 2012, to $3.4 billion, according to data released today by the Interactive Advertising Bureau.

That was up from $1.6 billion in 2011.

Mobile spending accounted for 9 percent of all online spending last year, a new high mark.

Those numbers include tablet advertising as well.