" my grandson is a U.S. Marine doing a training in the desert where the only civilized item is their phones but no wifi. "
GIven this information, I assumed he was in the Middle East , so you might understand why my answer didn't make sense to you.
IF you switch to the new Verizon plan and backdate your plan, you will get more data for the same $100. Line fees will be $20 for out of contract phones and $40 for in contract. It should not increase your regular bill.
ASk for for the extra large plan.