I hear that the phone needs a sim card for basic functionality. I could be wrong. This means you need some kind of a phone card which you can only get through a plan.
No, you MUST get it with the plan. People always wanna get the iPhone because it's $200 WITH a plan. Without, it's $400. You're better off with an iPod. Just wait for your mom to get a job and then buy the iPhone or just get an iPod and buy a cheaper phone.