To simplify my story, let's assume my mobile app (iOS and Android, developed using Phonegap) allows the user to store stuff in containers. I'm offering it for free for users that need up to 6 containers.
Now I want to allow users that need more than 6 containers. I want to charge $1 for each container used per month.
What's the right way of doing that? In-app Purchasing is probably not the right way to go, because I want to charge monthly - and auto-renewable subscription might not work because I don't offer a flat rate for the subscription (each month could have a different subtotal).
I noticed a lot of apps are getting the user to provide credit card / paypal on registration, but I believe they are allowed to do that since they are selling real-world goods/services (I'm not).
Needless to say, while I'm not very happy giving Apple/Google a 30% cut of my entire income, I definitely don't want to do anything that might breach their terms and upset them.
Thanks, Joseph.