Google and Apple would be wise to work with telcos in developing more robust carrier billing infrastructures. It has been done before with Symbian, and is a heck of a lot better than gift cards, imho.

Fraud by telcos needs to be kept in check obviously, possibly by issuing digital invoices/receipts that people can store and check against their monthly bills. Parents who foot their kid’s bills might not be so keen, though I suppose you could apply some form of parental control for purchases.

Just my 2 cents.