Unlimited talk. Unlimited texting. And 500MB of 3G/4G data per month. So your total cost of operation -- for the first year, anyway -- is $0. That's "zero" with a "nothing" after it. The only charge you might incur is if you go over your 500MB cap, at which point you'll pay 2.5 cents per megabyte.
I'm not a math guy, but my calculator informs me that that works out to $2.50 per additional 100MB. So even if you burned through, say, 1.5GB each month, you'd end up paying a very reasonable $25.++