Ovum, a technology industry consultancy, says that although iPhones will remain as the top-selling high-end smartphone brand in the next five years, it faces a strong challenge from handsets based on Google's Android platform.

The research firm says that total mobile application downloads in the Asia-Pacific region are expected to reach 5.3 billion by 2015. Ovum predicts that Apple's share will be at 11 percent or about 597.15 million.

In a statement, Adam Leach , Ovum's principal analyst The iPhone 4 is expected "to face much stiffer competition than its predecessors."

"The rise of Google Android over the last two years has been phenomenal and is allowing manufacturers to create appealing alternatives to the iPhone, critically at cheaper prices," he said.

"This may ultimately be what puts the brakes on unlimited iPhone growth."