IowaCowboyWant to go back to IowaPremiumReviews:
Ask if you could buy the data card at full retail. When I went from 3G to 4G, I was forced to take a 4G plan. I had the promotional 3GB/$35 plan on a MiFi 2200 and had to give it up when I went 4G and had to buy the 5GB/$50 plan. I now have the ZTE Jetpack on a share everything plan.
I am pretty sure that they will not allow you to keep unlimited but if they do, you'll run the risk of being kicked off their network for excessive data usage as per the AUP and you'll hit their undefined cap pretty quickly on 4G. I would switch to their capped plans because they consider excessive usage on the old unlimited to be an AUP violation and you'll run the risk of being banned from their network and they will charge you the ETF. With the new plans, you'll run the risk of overages (which is better than ending up blacklisted).