@Ell
No, this is an add-on, these is in addition to your regular data allowance. It will be used only after you use up your data and what ever is left will not expire but stay with you until you use it up. It's a great cushion to ensure you are not cut off when you use up your plan data, or those months when you need a bit more but you don't want to switch (and possibly lose if it's not offered anymore) your plan
