The new plans provide 10GB of 4G LTE data per line, starting at $100 per month for two lines. Subscribers can add a third line--also with 10GB of its own data--for $20 more per month. For those who sign up by Labor Day, T-Mobile is giving away a fourth line at no extra charge (though taxes and fees still apply).
By comparison, Verizon charges $170 per month for two lines with 20GB of shared data, and AT&T charges $180 per month. For a plan with four lines and 40GB of shared data, Verizon and AT&T both charge $360 per month--three times the price of T-Mobile's current promotion.
Sprint comes a bit closer, at least new subscribers, with a current offer of five lines with 20GB of shared data for $100 per month. Normally, Sprint charges an additional $15 per line access fee, but is waiving that fee for new subscribers until September 2016.
T-Mobile's new plans will launch on July 15 for both new and current subscribers, and while they're billed as limited-time offers, there's no set expiration date. Subscribers will get the same benefits as other T-Mobile plans, including mobile hotspot use, rollover data, free overseas texting and data, and free roaming in Canada and Mexico. As with most other T-Mobile offerings, these plans don't include the cost of a smartphone, which can be purchased in full or paid off in monthly installments.
The impact on you at home: Keeping track of T-Mobile's various promotions can sometimes be a confusing affair, especially when a new deal seems to be at odds with previous ones. But for people who expect to use a decent amount of data every month, this new promotion is an unambiguous bargain.