U.S. Cellular announced an end-of-the-year deal to reward both new and existing customers with an offer that just screams savings: a discounted 4G LTE unlimited plan.

Through Jan. 31, U.S. Cellular subscribers can switch to an unlimited 4G LTE data plan for $40 a month.

The limited time offer is available to both current customers and new subscribers with a two-year contract, though they will have to switch back to one of U.S. Cellular's standard plans after the promotion ends in January.

The catch is that the deal is only available with a 4G LTE capable phone for users in U.S. Cellular's 4G coverage area. That limited area only extends to parts of certain 14 states, so while it's not a national offer, it's still a pretty sweet deal.

Unlimited redefined

It appears that the unlimited part of the plan refers to unlimited voice for calls, and U.S. Cellular hasn't specified whether there is actually a data cap on the plan. The carrier's regular 4G LTE plans have data caps at 2GB, 5GB and 10GB.

With the promotional plan users will also have the option of adding data tethering to their smartphone for an additional $20 per month.

To complement the promotional plan, U.S. Cellular is offering a $100 rebate on 15 of its smartphones, including both 4G capable and 3G models.

For 4G capable handsets, the rebate applies to the Samsung Galaxy S3 in both 16GB and 32GB variants, the 16GB Galaxy Note 2, Motorola Electrify M, Samsung Galaxy Metrix 4G and Samsung Galaxy S Aviator.

Even if the promotional plan isn't truly unlimited data, the $40 monthly price is a nice discount from U.S. Cellular's standard $69.99 per month rate for just unlimited voice.

If you're already a U.S. Cellular subscriber, it's the perfect opportunity to save some cash going into the new year.