Well, I'm being facetious, but it's been my experience that cats don't do anything unless they want to. Not one thing, no matter how much you hope or how nice you ask. Nothing, unless they want to.
As for the purring, usually occurring when stroking or gently petting a cat or kitten, that's voluntary. Not all cats will purr, but those that do are generally indicating contentment.
Meowing is definitely voluntary and purposely communicative. Lotsa luck figuring out what they're saying...
I truly love cats.