Maybe I have forgot some fscommand2 commands, but I think there is no command to setup the device's speaker volume via actionscript.
I have noticed that different nokia devices have different behaviour related to its volume keys. For example, a standalone app in a N95 reacts to the volume keys (in the device's right side), but the same application in a Nokia 6120 doesn't react to those keys. Both devices are FL 2.0 enabled and are S60.
I know that this is not a big issue, but since there are no way to increase or decrease the device's volume level via action script (you only can get the max volume level and the actual volume value) I think this kind of things should behave in the same way for the maximum number of devices.