T-Mobile today announced a new two-line family plan option that provides unlimited talk, text, and data services for $100 per month. Additional lines (up to eight more) can be added for $40 per month. T-Mobile says that this new plan is the only one to offer unlimited data along with a multi-line discount. The $100 per month cost of service for two lines covers just the phone service, and customers that purchase phones from T-Mobile will also likely have additional monthly payments for the phones that are separate from their phone plan. The carrier is offering the plan as an option to both existing and new customers starting tomorrow.

T-Mobile is quick to point out how much its new unlimited plan undercuts plans from AT&T and Verizon that offer large amounts of data use per month. The carrier says a two-line family plan from Verizon with 20GB of shared data would cost $180 per month, while AT&T's 30GB two-line plan runs $160 per month.

T-Mobile's plan offers more data at $60 to $80 less per month than family plans from Verizon and AT&T

If you're not interested in unlimited data, T-Mobile is also resurrecting its $100 10GB plan for four lines of service. Each line on this plan receives unlimited talk and text services and 2.5GB of high-speed data per month. (T-Mobile will slow down, or throttle, the data connection if a line goes over 2.5GB in a month.)

Unlimited data has become a bit of a unicorn in the US, with Sprint and T-Mobile being the only major carriers still offering it to their customers. Sprint's unlimited plans are only available to individual lines, so a family looking for unlimited data will pay significantly more than with T-Mobile's new plan. Though T-Mobile has been aggressively upgrading its network and cutting its prices, it still doesn't offer the same level of coverage as AT&T and Verizon, especially outside of urban areas, so those looking to jump on one of these new plans are best advised to check their local area's coverage maps before signing up.