Amazon may have sold half a million Kindles last year, if one analyst's estimates are accurate.

Amazon has never revealed sales figures for its e-book reader, launched in November 2007, only ever stating that it was "happy" with the level of sales.

Back in August 2008 TechCrunch reported that Amazon had shifted 240,000 units of the device, citing "insider info", but Citigroup analyst Mark Mahaney has come up with a new way of estimating sales.

Mahaney has analysed figures from Sprint, the US wireless carrier that provides the Kindle's EV-DO connectivity, and come up with 500,000, estimating that it could be a £1.2 billion a year business for Amazon if users buy one e-book a month.

Amazon is heavily tipped to unveil its new, improved version of the Kindle, at a press event next week - we'll bring you more news nearer the time.