Amazon debuts Kindle Unlimited on any device for $9.99 a month on Friday debuted Kindle Unlimited,allowing customers to access more than600,000 Kindle books, and listen as much as theywant to thousands of Audible audiobooks for $9.99 a month.

Kindle Unlimited subscribers will also receivea complimentary three-month Audible membershipfrom all Kindle devices or with Amazon'sfree Kindle reading apps.

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"With Kindle Unlimited, you won't have to think twice before you try a new author or genre—you can just start reading and listening," Russ Grandinetti, Senior Vice President for Kindle, said in a press release.

—By CNBC staff