Apple will sell 13.5 million Apple iPhones by the end of next year, analyst firm RBC Capital Markets has predicted.

Previous forecasts have suggested that Apple will sell 8 million Apple iPhones by the end of this year. This would put the company well ahead of its target of selling 10 million phones by the end of 2008.

RBC's figures also show that sales of the iPhone are nearing the million mark, with 950,000 devices sold so far.

Apple may introduce higher-memory (16GB) iPhones, as well as higher-resolution 480 x 720 pixel displays. There are likely to be other upgrades as well to the existing models, accompanied by lower prices to keep demand up, SeekingAlpha speculated.

3G/HSDPA-enabled Apple iPhone

Of course, launching a 3G/HSDPA-enabled Apple iPhone for the European, Asian and Canadian markets is still on Apple's roadmap.

Another survey today revealed that one in three people are thinking of buying an Apple iPhone. Lightspeed Research asked 39,000 US adults at the time of the iPhone launch whether they would buy the device. Some 8 per cent said they would buy one within three months, while 22 per cent said they planned to buy one at some point.

We'll get more info on how well the Apple iPhone is selling when Apple releases its quarterly financial report on 25 July.