Google has made its Book Search function available to Apple iPhone and T-Mobile G1 users. It joins a growing group of network operators and content providers that are putting books on mobile phones.

Google originally began digitising books to make them accessible over the web from a PC through its Book Search service. Beginning with scanned images of the books' pages, Google used optical character recognition (OCR) technology to extract and index the text to make it searchable.

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On a PC, someone searching for a quote is shown the high-resolution image of the corresponding page, but those pages won't easily fit on the small screen of a mobile device, so for the new service Google sends just the text, as it would for any other text on a web page.

The new service opens up mobile access to 1.5 million public domain books in the US and half a million outside the country, Google said.

The technology is still being perfected, so automatically recognised texts can include errors. If you hit "patches where the text seems, well, weird, well, you can just tap on the text to see the original page image", Google said in a blog.

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Books can be searched for, or located via a number of categories, including adventure, classics and drama. Titles available on the mobile version include classics such as Oliver Twist, Shakespeare's King Henry V, The Jungle Book and The Hunchback of Notre Dame.

Google isn't the only company interested in putting books on mobile phones. Amazon is working on making titles for its popular e-book reader, the Kindle, available on a variety of mobile phones, according to the New York Times, while mobile operator Vodafone recently launched 'Books on Mobile!', which offers books in both text or audio format for between £5 and £15.

The growing popularity of dedicated readers have made the mobile industry realise that there is an opportunity here - just like it in the past has put music and games on mobile phones to turn them into a one-stop-shop, according to Paolo Pescatore, analyst at CCS Insight.

See also: Google Book Search to put millions of titles online