T-Mobile is sweetening its ONE plan this Valentine's by offering a free line of service when you add a new one to an existing family plan or start a new one. That may sound slightly confusing, but what it really boils down to is that you can get a T-Mobile ONE plan with 4 lines for $35 per line (that's $140 total), instead of the usual $40. T-Mobile's ONE plan already comes with unlimited 4G data (deprioritized at >50 GB), tethering, data roaming in 140+ countries, and a standard Netflix subscription.

The catch seems to be that, if you already have a family plan, you have to add a new line to get the second one free. In other words, if you're already on a family plan with 4 lines, you probably won't be able to get 4 lines for the price of 3, but you will be able to get 6 for the price of 5. Still, that's a pretty good deal for new customers or if you were already considering expanding your current family plan from 2 to 4 lines.

T-Mobile says this is a "limited-time offer," but it doesn't specify when it'll expire, so if you'd like to take advantage of the promotion, you should probably do so sooner rather than later.

Edit: A reader says that a representative confirmed the deal expires on the 15th.

PRESS RELEASE