What is "A Handler Is Needed To Use This Content Type"?
The short answer is that your phone can not handle that type of file.
I suggest trying a different type. If you tried an MP3, maybe a MIDI would
work better.
The long answer is that your phone's browser is able to be extended with
plugins and one was not yet loaded to handle that media type. As far as
I know, there are no plugins available for loading by users to any phone.
The ending result is that you're stuck and your phone does not and will
not support that type of file.