I'm with ATT right now. However, I don't want to lose currently unlimited data plan, so is that possible I can active my new iphone 4 not through att. thus i don't have to change to the plan(200mb/$15) I selected when I pre-ordered this iphone?
People with unlimited data plans are grandfathered in, even if they upgrade their phones. You should just call them and make that change before you activate. Hopefully they will not tell you you've already lost your grandfathering.