Questions about my Sprint cell phone?

[Sef]

In the app world, I've never bought anything. in the sprint music Store I have bought some music. They were like a dollar or 2 per song. It didn't ask for a credit card number so I assumed the price would be tacked on to my phone bill. When the time to pay my bill came, I didn't notice any increase to the bill, I didn't remember to check. Is my assumption correct? As for my 'spending limit', it'll say 'I have x amount left to spend, I've spent x amount so far'. Like I said, I've never bought anything. Why would it say I've spent some? I have the unlimited 69.99 everything plan, and I have a blackberry curve 8530