Control the volume

Hi everyone, here's my doubt:

I'm developing an audio player with different tools, being one of them to control the volume of the audio file. I just have had problems with this function. I wrote two different functions, volup() and voldown() and then I just wrote:
canvas.bind(key_codes.EKeyRightArrow, volup)
canvas.bind(key_codes.EKeyLeftArrow, voldown)
Well, this works on the emulator but not on the mobile phone (I'm using a nokia N95).

Anyone knows where is the problem?

Thanks in advance :-)