The headlines pop out of the pie charts at right, drawn from data released by Gartner, Inc. Thursday.

• Nokia’s (NOK) Symbian, Research in Motion’s (RIMM) BlackBerry OS and Microsoft’s (MSFT) Windows Mobile continue to lose share in the worldwide smartphone market.
• Apple’s (AAPL) iOS grew modestly in Q2, from a 13% market share to 14.2%.
• Google’s (GOOG) Android grew explosively, from 1.8% in Q2 2009 to 17.2% in Q2 2010. Android has now overtaken RIM to become the No. 1 smartphone OS in the U.S., and has overtaken Apple to become No. 3 worldwide.

What the pie charts don’t show, however, is that these are shares of a rapidly expanding universe. Mobile phone sales to end users grew 13.8% year over year according to Gartner, and smartphone sales accounted for 19% of them, a 50.5% increase.

So although Apple’s share of the smartphone market only grew 1.2 percentage points last quarter, its sales to end users, as Gartner measures them, were up more than 64% year over year, from 5.3 million to 8.7 million.

“Apple’s sales would have been higher, if it had not had to face tight inventory management in preparation for the arrival of the iPhone 4 at the end of the second quarter of 2010,” according to Gartner.  “We expect that a wider global rollout of iPhone 4 will sustain Apple’s sales momentum throughout the second half of 2010.”

You can read Gartner’s full report here.

[Follow Philip Elmer-DeWitt on Twitter @philiped]