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. Once that's done, you just have to upload the final bill from your current carrier, showing the early termination fee or remaining balance you paid to cancel. AT&T will then take that amount, subtract the total amount of the Buyback from your current device, and send you a Visa Prepaid Card for the total, which can be up to $650.

Now, do that for each line on your plan. Be aware that it takes roughly four to six weeks to get the Visa Prepaid Card back, so don't spend the upfront funds on new phones expecting to see the reimbursement within a few days.

Ready to get started? Head here — you can even check the Buyback value of your current phone before making the leap. Simple.