Yeah...you might have to call Customer Care and provide them with the updated phone's IMEI to remove the data plan. And if you give up an unlimited data plan you probably can't get it back...you'll have to go with one of the tiered plans.
Yep, that's basically it, but as BrianfromNO already stated, you will have to remove the data plan from your account if you want to discontinue your use with it. Be aware that QMD (Quick Messaging) devices may also have to have a mandatory messaging plan added to it if you were to get a QMD feature phone. If you're just going to stay with a basic phone, then you should not have any add-ons to your account.