We are thrilled to offer iPhone 5 on the nations largest 4G network. Weve worked with Apple since the original in 2007 and this is hands-down their best phone yet, said Ralph de la Vega, president & CEO, AT&T Mobility. We offer customers the flexibility to keep the iPhone data plans they already have or choose any of our individual or new Mobile Share plans.
The "plan I already have" is for 3G, so I'm not sure its 100% clear that I will get unlimited LTE.
See post #2
This is great news, but it’s important to note your plan isn’t truly unlimited. When you hit the new 5GB limit, AT&T will throttle your 4G LTE speed for the remainder of your billing cycle. Prior to these changes, customers were throttled after 3GB of data usage.