Att uverse hbo subscription?

I have att uverse cable and do not have a subscription to hbo or showtime movie channels. However, when i browse the on demand section i am able to view the hbo movies and tv shows but it shows no prices. If i were to watch a movie, would it automatically subscribe me to the feature and put it on my bill every month until i cancel or would it be a one time movie fee?|||Cinamax and hbo had a free weekend free 24th thru the 27th. It was free for a few days woohooo!!