Sales of Apple's iPhone will continue to help the rapid expansion of the global smartphone market, according to a market research firm.

Figures from IHS iSuppli show that Apple's market share in the second quarter of 2011 was 18.4 percent, putting it ahead of Samsung, Nokia, RIM, HTC, Motorola and Sharp.

The second quarter of 2011 was the first time that Apple had been the world's largest smartphone brand, boosting its shipments from 18.6 million in the first quarter to 20.3 million. It shipped 8.4 million units in the second quarter of 2010.

Apple was helped, of course, by a 31 percent decline in shipments at longtime market leader Nokia.

How Apple fares in the future, though, could depend on whether it focuses on the high end of the market, or introduces a lower-cost iPhone in order to target developing markets.

“With the refresh of the iPhone line, along with continued expansion of Apple’s sales channels, we expect the company to continue to maintain its momentum in the smartphone market in the third quarter and beyond,” said Francis Sideco, senior principal analyst, wireless communications, for IHS.

“However, Samsung has been coming on strong during the last few quarters, driven by its participation in both the high- and low-end smartphone segments. One of the key indicators of how the smartphone competitive landscape will evolve during the next six to 12 months will be whether or not Apple will continue to stay exclusively in the high-end market—or if it will introduce a low-end model.”