I'm trying to find out if it's allowed to use alternative payment platforms for iOS, Android and WP7. By alternative I mean not the payment solution provided by the company.
I'm pretty sure for iOS you have to use Apple's billing platform. Is that also the case for Android (what about Amazon's Android Market?) and WP7?
You're free to use any other billing platform for Android. As for Windows Phone 7, Microsoft don't offer in-app purchases, so obviously here you have to use a 3rd party billing platform. (Inn-app purchases been enabled with Windows Phone 8)
However, it's much easier for users to use iTunes/Google Checkout, since their CC is already integrated here.