POD Cast Help

I'm not sure exactly where this question fits in, but I'll ask it here since I listen to POD Casts on my iP6. I'm new to Apple, iOS, and iPhone so here's my question:

1) when you download POD casts to your iPhone via wi-fi and choose to listen to them later, since they're already downloaded to your phone, does it tap into your data if you're not connected to wi-fi when you listen to them?

Any information you can provide will be helpful,
Thanks!