Can I use my iphone without the 20 a month service plan?

I'm getting an Iphone in a few days, but I won't be able to add the unlimited data plan for a little while. It's unlocked and jailbroken. I'm planning on putting my current ATT sim card in it when I get it.

A. Is it possible to do that with a normal att card if it's unlocked?

B. Can I use the iphone without the unlimited data plan?

C. If I can, how do I/can I disable all the features that would use up all that data. Not having the plan would get pretty expensive, I would think, and disabling it seems to be the best route if it's possible.