For the first time ever, worldwide smartphone shipments outpaced those of feature phones in the first quarter of 2013, while Apple's market share dropped to below 20.

Apple reported a 6.6 percent year-over-year increase in sales for the first quarter of 2013, but the iPhone's growth was apparently not strong enough to stop rival smartphone makers from grabbing more market share.

Apple reported iPhone sales of 37.4 million units during its quarterly earnings conference call for the second fiscal quarter of 2013, up from 35.1 million in the previous year. That translates to a 6.6-percent growth rate. According to market research firm IDC, the last time Apple posted year-over-year growth in the single digits was back in the third quarter of 2009.

According to IDC's Worldwide Quarterly Mobile Phone Tracker, Apple's worldwide share of the smartphone market dipped to 17.3 percent at the end of the first quarter, down from 23 percent in 2012, placing it on the second spot behind Samsung. Apple was the only top-five smartphone manufacturer to see its market share drop during the period.

However, in terms of total mobile phone shipments, which include feature phones, Apple's performance is slightly better, as the iPhone's share grew from 8.7 percent in 2012 to 8.9 percent.

Samsung, meanwhile, continues to be the worldwide leader and grew its share of the smartphone market to 32.7 percent on shipments of 70.7 million units, marking a 4 percent growth. During the same period the previous year, the company saw 60.7 percent on shipments of 44 million units. Total smartphone shipments reached 115 million, a 27.5 percent share of the total mobile phone market.

The biggest surprise, however, comes from third-place vendor LG, who saw the biggest year-over-year change in smartphone shipments. LG saw a 110.2 increase, from 4.9 million to 10.3 million units. On the other hand, the company still has a relatively small market share, with only 4.8 percent.

Huawei and ZTE round out the top five smartphone vendors, with shipments of 9.9 million and 9.1 million units: 4.6 percent and 4.2 percent of the market, respectively. Overall, smartphone shipments hit 216.2 million units in the first quarter of 2013, accounting for 51.6 percent of the 418.6 million total phones shipped.