Well, actually, at first, I thought that was what the Fizz wallet was for, not for the "pay as you go". And, yes, I would have like that!
Being able to "fund" the balance of the account, and then, when the cycle begins, the money is taken from that balance. Yes, this is something I was doing before with my other prepaid service, and I liked it.
Like many people answered, I don't like being tied, or paying in advance either. But, I do like the opportunity to put the money there when I wan't. And that's how I understood what you meant with your question.
This definately would be a nice feature to have at Fizz!