28% of smartphones in the US are sold to people who earn less than $30,000 a year

"As U.S mobile phones sales transition to predominately smartphones, buyers have become significantly older and less affluent.  For the third consecutive three month period ending February 2015, sales among consumers earning less than $30,000 per year grew by more than 50 percent.  This demographic is now the largest segment of the smartphones market, accounting for 28 percent of all sales.  In contrast, sales among consumers earning more than $100 thousand a year increased by just 24 percent. For the three months ending February 2015, buyers aged 55+ also represented 28 percent of all sales, up 24 percent from a year ago, and were the fastest growing age segment of the population.
Over the three month period ending in February, overall sales of mobile phones rose 28 percent compared to last year, while smartphone sales increased 35 percent. During the same three month period, the share of sales for non-smartphones declined to just 14 percent."

Source:  Press release from NPD, 21st April 2015