We bought out the Verizon plan for $175 and switched to Millenicom and have 20GB for less than 10GB with Verizon. No worries about running over the penalties from Verizon are steep. Check the many complaints by Verizonwireless customers on the company's own community forum for overbilling of these "overages".
Wow, that's a lot of money to spend to move to another service that you still have to pay plenty for. $175 for the buyout plus the new hardware cost, plus the start up fees and you are into it for about $300 (or more) before you download your first bit of data.
I was with Verizon, dropped them for Millenicom and then dropped Millenicom to return to Verizon when they came out with the Share Everything plan. I monitor my usage in real time so there would never be any reason to incur an overage. If I am using more than I had planned for I just go online and change it. It costs $10/2GB. If I don't use as much as I expected I go online and reduce my allowance saving me $10/2GB. I have a reminder set on my calendar in case I forget as I can change my plan right up until the last day.
I would never use 20GB but that certainly might not be the case for you and I mean no offense and do not mean any slight to the option you have chosen.