In a blog post, Microsoft stated:
"Today on Windows 10 we offer traditional debit and credit card options as well as PayPal, Alipay, app gifting, gift cards and Bitcoin (US only). Later this year we will enable PC and tablet customers to pay via their phone bill with carrier billing – now available for our Windows Phone customers via 100 carriers across 57 markets. This represents a reach of 3 billion mobile subscribers; an increase of 40 carriers YoY."
Microsoft points out that 88% of the world's population does not currently use credit cards, so the option to enable carrier billing on PCs and tablets should allow for a big revenue boost for Windows 10 app publishers.