The US accounts for 21% of global mobile data revenues

"The US market generated $67 billion in mobile data revenues in 2011 accounting for 39% of the overall revenues for the country. The mobile data market grew 4% Q/Q and 19% Y/Y to reach $18.6B for the quarter. For the year 2012, we are forecasting that mobile data revenues in the US market will reach $80 billion.
The US market accounts for 5% of the subscriber base but 17% of the global service revenues and 21% of the global mobile data revenues. It also accounts for 40% for the global smartphone sales.
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Mobile data traffic growth continued unabated doubling again for the 8th straight year. We expect the mobile consumption to double again in 2012. Data now constitutes over 85% of the mobile traffic in the US."

Source:  Data from Chetan Sharma Consulting, reported on their site, March 2012