Instead of recording a voice mail greeting with your own voice, you can choose from several premade voice types that will read out a typed greeting to incoming callers. The voices aren't perfect, but the typed greeting features add variation and can be pretty funny when used creatively.
If you want to call your friends who don't have the Libon app, you'll only have 60 minutes of calling time per month. Divided up among all your calls for an entire month, 60 minutes isn't much at all.