I am a current AT&T customer with a year and a half or so left on my plan. I have purchased phones before and just had them activated or switced sim cards during my plan, you just had to pay full price for the phone. So, can I do this with the new iphone? And is the 3G unlimited plan necessary? Do i have to have this plan in order for my phone to run? Or an i just use the phone part and unlimited texting like i do on all my other phones?