Edit: Android now supports in-app billing!
Original question:
It looks like Android won\'t natively support in-app purchase
Looks like Paypal has launched a library for accepting in-app payments. See here. Not sure if this system violates the T&C though.
For implementing in-app purchases in Air applications you may use third-party libs (Adobe AIR does not support In App Purchases for any platforms out of the box). For example, developed by Milkman Games (unfortunately, they are not free)
It is against the Android Market Developer Distribution Agreement to take in-app payment:
3.3 ... All fees received by Developers for Products distributed via the Market must be processed by the Market’s Payment Processor.