There's a simpler method, if you already have a panel /aircraft with callout sounds. Some panels have invisible callout 'gauges' that activate at particular altitudes. If you look in the appropriate panel.cfg file, you will normally see them in the main window gauge listing - normally easy to identify as the have 'callout' as part of the name. (Same for GPWS.)
Copy and paste this line into the panel/aircraft you want the callout in (remembering to change the gauge number to the next sequential one), and there you are.
If you don't have the gauge, you should be able to locate a free-standing callout gauge on one of the main download sites.
