By Iain Mackenzie
Newsbeat US reporter
Kindle 2 is only on sale in the US and sells for $359 (£240)
Amazon has launched a version of its Kindle e-book reader for iPhone and iPod Touch.
The software allows users to download titles they have bought from Amazon's online store.
Previously, customers needed to buy a dedicated Kindle device, which sold for around $359 (£240) and was only available in the United States.
The iPhone/iPod launch is expected to dramatically increase Amazon's e-book sales.
Kindle is thought to have around a quarter of a million users.
The latest figures from Apple show more than 13 million iPhones have been sold globally, opening a much larger potential customer base for Amazon.
The Kindle software will be made available through Apple's app store.
The system uses a technology, known as Whispersync, to synchronise users' purchases between their online account and handheld devices.
Last month, Amazon launched the second generation of its dedicated Kindle reader.
However, it has yet to go on sale outside the United States, partly because of the different wireless technologies used around the world.
The launch of Kindle for Apple devices makes it more likely that the Kindle service will now roll out globally.
However, Amazon says the application will only initially be available to users in the US.
Amazon boss Steven Kessel has said that the company's goal is to make "every book, ever printed, in any language" available for download to Kindle.