Here’s how it works: for $20 a month you get all the basics (talk, text, Wi-Fi tethering, and international coverage in 120+ countries), and then it’s a flat $10 per GB for cellular data while in the U.S. and abroad. 1GB is $10/month, 2GB is $20/month, 3GB is $30/month, and so on. Since it’s hard to predict your data usage, you’ll get credit for the full value of your unused data. Let’s say you go with 3GB for $30 and only use 1.4GB one month. You’ll get $16 back, so you only pay for what you use.
I think I can move providers! More here.