That's half the regular price and an unusually good deal, but there's a small catch. //

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

Now, if you're willing to pay just a bit more, you can get a similar deal from AT&T: The online-only AT&T Prepaid 8GB Promo Plan costs $300 and buys you 12 months of service. (Taxes and fees are extra.) That's literally half the price of the same plan charged monthly. //

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, which is available until Oct. 21, you'll need to either buy a phone or bring one that's compatible with the network.