AT&T's 'secret' prepaid plan is great for those who don't need unlimited data

For the last few years, Mint Mobile has courted new customers by offering low rates -- but with the stipulation that you have to buy service in bulk, prepaying for anywhere from 3-12 months. For example, a $240 payment will buy you 12 months of the carrier's 8GB plan.

If you're willing to pay a bit more, you can get a similar deal from AT&T: The online-only AT&T Prepaid 8GB 12-Month Plan costs $300. (Taxes and fees are extra.) That's significantly less than what AT&T charges for a basic unlimited plan. (Make sure to click Multi-month plans to find this option; Monthly plans is selected by default and doesn't show it.)

I first spotted this plan about a year ago, and it appears very little has changed since then. I still don't see it advertised anywhere, and it's still not prominently mentioned on AT&T's home page; you have to drill into the Prepaid section to find it. As noted above, it's an online-only offer: If you stop by an AT&T store hoping to sign up, it's possible the sales folks won't even know about it.

Read more: Verizon vs AT&T vs T-Mobile: Choose the best 5G carrier

As you'd expect, the plan affords unlimited talk and texting -- not just in the US, but also in Canada and Mexico. (Mint Mobile, for its part, lets you make calls to those countries, but calling from within them costs extra.) It includes 8GB of high-speed data (it's not clear if 5G is included or not), and any unused data can roll over, though only for one month. You get a mobile hotspot as well, same as with Mint: It draws from your monthly data allotment.

The Canada/Mexico and rollover benefits give AT&T a slight edge over Mint Mobile, but the big appeal for some folks will be AT&T's network. Depending on where you live, it might be a better option than T-Mobile's, which is what Mint uses.

To take advantage of AT&T's deal, you'll need to either buy a phone or bring an unlocked one that's compatible with the network. You'll pay $4.99 for a SIM card and $300 for the 12-month plan, bringing your total to about $305, not including taxes and fees. That could add another $30-$40 to your out-the-door total, because remember this is for 12 months' worth of service, not just one.

What do you think? Is this a sweet enough deal to convince you to choose AT&T over Mint Mobile? Or AT&T over AT&T, assuming you were paying monthly before?

Read More: All the latest AT&T coupons

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