...I haven't found the answers anywhere and I've been looking. I have a 1st gen iphone with unlimited data on at&t (not on contract). If I buy a new unlocked iphone will my data plan remain the same (month to month $25 for unlimited data) if I continue to use my old sim card? Will it run 4G or just the Edge network that I can access with my old phone? What if I buy a 3Gs off of someone on Craigslist? Do I just use my old card, or will AT&T automatically change my data plan? Sorry for the stupid questions and thanks for your thoughts!