Motorola is making a shift in their preferred operating systems for their phones. As of now, the company is developing all of its advanced features on Linux first.
Motorola has made the move largely to take advantage of all the developers out there who are developing and improving the open source software. It is also a way to differentiate and compete with Nokia, who is the key backer of Symbian. They are not giving up on Windows Mobile or Symbian OS, however: Motorola will still be making devices that work on both systems as the market calls for them.
Motorola is not new to Linux. They first sold a phone running on Linux in 2000 in China, because the growing market liked the OS. Linux has a small market share in most countries, especially outside of Asia, but this move by Motorola will help to establish the OS, and will help to improve and strengthen the developer community since they will have a much bigger market to provide products for.