"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."
Here you can see how Windows Mobile stacks up against some other mobile platforms in terms of openness. I've never understood the "free, as in beer" idiom. I don't drink beer, but I've been around people that do, and they always seem to be paying for it, both before and after drinking it.
