Whatsapp only had a subscription fee for android users, and I don't know anybody who ever paid for it. They would keep giving you more and more free time; free subscription time would never run out. I imagine it ran out for some users, but I don't know what the criteria was. Perhaps for users in certain countries? Or for users with lots of iphone friends?

On the other hand, iphone users had to pay for the app upfront to download it off the app store.