There is a device which has output impedance 150ohms. If my headphone has either lower(30ohms) or higher (400ohms) impedance can I use it or sound will be too low/high and it will be unsable?

Also, the volume higher/lower is being done by the device by changing the impedance or by changing voltage?

Thanks

EDIT: device outputs: 35mW in headphone output jack, impedance 150ohms. 

-Can i connect my headphone of it will damage it?

-Will it work?

-When it says 35mW what does it mean? 0mW no sound, 35mW volume max?