Changing carriers can be a real pain. In fact, a lot of people probably stick with their current carrier just to avoid the headache — even if they're unhappy with the service. AT&T wants to ease the pain and frustration a little bit by offering users who switch from another carrier up to $650 in credit per line. For a family, that can potentially be a huge savings. Here's how it works.

You buy a new smartphone from AT&T on a Next plan (both the phone and plan are your choice, of course) and port your existing number over. Check out the AT&T Buyback website and trade in your current smartphone — keep in mind that it must be eligible and not all phones are worth the same amount.

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