It would seem not just any device. Accoding to PC MAG......
"Bezos said Amazon was open to licensing its content to other e-book manufacturers, provided they provide the type of customer experience dictated by Amazon.
Any competing device selling Amazon books, for example, must include the Whispersync technology, which lets users return to the page they were reading, whether on the Kindle or the iPhone."
http://www.pcmag.com/article2/0,2817,2348798,00.asp