How exactly does AT&T Next work?

I'm planning on getting a new phone probably with AT&T because I currently have a phone with T-Mobile and let's just say they don't have the best service ever. I would really like to get an Iphone 5s with AT&T without a contract and without having to pay a lot of money. I heard about AT&T Next but I'm not really sure how it works. If I were to get an Iphone 5s on AT&T Next, around how much would I end up paying for the phone and how much would the plan cost if I wanted unlimited talk, text, and data as well as international calling (which is $10 a month I believe). If you have any information at all, I would greatly appreciate it.

The people at A T and T will be very happy to tell you how much your bill will be

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