After some research, I am happy to inform you that we don't currently have any plans to remove the Unlimited Data plan being grandfathered from customers that switch to an LTE device. In other words, at this time, you may keep the unlimited data plan once you switch. Please continue to check in with this information as this this might change in the future, although we don't have future information regarding the grandfathered Unlimited Data Plans.
Translation: We don't have any LTE capable phones nor does our network even support it so we're gonna ignore the question. They don't currently have any plans to change their policy but this can change in a day.