The tone library uses interrupts. The way interrupts are used on Amtel (Arduino processors) is vastly different from how they are used on x86 processors (Galileo processor). The interrupt library has not been ported to date. But that is just one of the hurdles.
In addition Galileo has a relatively slow I/O speed (when compared with Arduino). Essentially, if you need to read an input or drive an output, more than a few times a second, the Galileo might not be able to keep up.
Just toggling a pin (which is essentially what you are doing in order to make a tone), you should be able to get up to 230Hz, which is audible, but this is just a free running script that constantly toggles a digital pin, no other code running at the same time.
https://communities.intel.com/message/208688#208688
There are two pins which can go faster. The thread above talks about that, and the speeds that can be achieved. Again this is code that is doing nothing but toggling a pin. If you need to run other code at the same time, it will not work.
In theory you could toggle a pin, at the right frequency and get a tone out.
It might be easier to get a USB audio device working. Although, I don't know of anyone who has done that.
