Nearly one in five (19 percent) mobile phones shipped in Q2 of this year were smartphones, says ABI Research.

The research firm revealed that 12 percent up on the first quarter of this year and a 50 percent increase on Q2 of 2009.

ABI Research analyst, Michael Morgan, believes the remarkable growth in the smartphone market is due to falling handset prices, which are often heavily subsidised by operators.

Apple's iPhone 4 was among the smartphones shipped in Q2

"One of the key remaining barriers to smartphone adoption in subsidised markets is now the cost of the data plan rather than the cost of the handset," said Morgan.

"The market is exploding but there are so many players and so many operating systems that the question becomes, 'Can this market structure be sustained?'"

Morgan said it's unlikely the market structure can be sustained, and "it needs to boil down to three or perhaps four key operating systems".

ABI Research said Apple shipped 8.4 million iPhones in Q2, three million of which were iPhone 4's. HTC also did very well, with shipments growing from 3.3 million to 5.3 million units the by the start of the third quarter

Despite RIM recently launching its latest OS, Morgan says: "RIM hasn't seen the full benefit of its OS launch yet," as its quarter-on-quarter growth moved only from 10.5 to 11.2 million shipments.

See also: 39% of smartphone owners regularly download apps