I lost my unlimited data plan when I upgraded and got a subsidized iPhone. Ultimately I decided that it makes more fiscal sense to get subsidized phones and pay for upgrading from my 2GB plan to 4GB or 6GB on the months when I go over.

Verizon makes it easy to increase your monthly data allowance for a month as long as you request it before the billing period is over. It automatically reverts back to your base plan for the next month.

They even send you an SMS as you approach your limit. It's as simple as a call or chat through their terrible website requesting a one month increase.