This application for Sony SmartWatch allows you to modify the music volume on your phone.

Press on + to increase or - to reduce the volume. The bar indicates the current value.

If you want the widget version, take a look at "VolumeWidget - Smart Extras?" (the touch area is smaller in the widget and less responsive).

Icons are from IconEden (http://www.iconeden.com)

LiveWare? extension for SmartWatch 1 (not tested on SmartWatch 2)