"Open operating systems, for most folks, means that the operating system is essentially free. The average computer user knows that Linux is free, as in beer, while Windows costs money. The case is the same for mobile OSes although, until very recently, the idea of purposely using an open OS has been a fairly nebulous concept.
To be clear open mobile OSes have been around for years, starting most prominently with the QTopia project that ran on ARM hardware found in many PDAs and phones. The Linux kernel plays well with almost any platform, making it ideal for small installations." Read more here: