I must have been living in the future all these years...
... because I've only ever paid for apps using my mobile phone bill.
Nokia has offered this facility for over two years (and it now costs nothing extra to the dev), and users of Samsung's Bada phones can also pay by bill in some countries. Nokia's PR claims that operator billing increases developer sales by 3x overall, but this rises to over 5x in some markets, so even after adjusting those claims for inflation, it's definitely good news for devs as well as operators.
Considering that virtually every operator in Europe already offers this service to customers who own a Nokia phone, I can't help thinking that whatever "complexity" they're talking about was more likely to have been reluctance on Google's part to hand control to someone other than Google.