Thought: iPhone 'slush pool' for making small payments practical

Just some quick notes. iPhone 'slush pool'
For small, fairly frequent payment amounts to work it needs to be low friction
No putting in ure iTunes password for each payment
The idea:
You have a 'slush pool'. A max amount put in at a time - a small amount like $5. You enter your password when u do this.
And you can use this to make small quick payments. Like paying 4 media content. 
Coz u don't enter password it's not as safe. Someone could grab your phone and buy stuff w/ it. But that's ok. The idea is tt this is a reasonable tradeoff of risk vs convenience.