The iPhone is not compatible w/ Alltel because they use CDMA and the iPhone operates on GSM. Think of it like the difference between a cassette tape player vs. a CD player.
I want to get an iphone. I have Alltel. If I get an unlocked iphone can I use it with my carrier? I've read a little bit of info about the unlocked iphones and they say they have sim cards that you can take out and use. How would this help me? Please help! I'm completely new to this stuff.