Simply put, if you choose to have overage protection ON for your data plan, after you use the amount of high-speed LTE data in the plan, you will still have access to unlimited 2G speeds thru the remainder of your bill cycle free of charge. 2G speeds are approximately 64 Kbps.
If you would prefer to have faster data speed, just log in to your Twigby Self Care account and TURN OFF Overage Protection for your data plan. With this setting OFF, you will then move to the next data plan. Once moved, you can then turn overage protection back ON so you don't continue to move up. It is completely up to you.