Starting March 1st, customers will be able to snag three lines for $100 (with fees and taxes included) on a One, Simple Choice or Simple Choice No Credit plan. And don't worry, if you've already got three or more lines, you can tack on another for free, according to the @TMobileHelp Twitter account. The promo doesn't have an end date yet, but customers who get in on it now will be able to keep their free line for as long as they're on an eligible T-Mobile plan.

So now, we wait and see how the other carriers will respond. The marketplace is super competitive right now, so consumers really stand to benefit from whatever happens next.