First, the plan itself is only good through March 31, 2018, at which point Sprint's former pricing goes back into effect: $60 per month for the first line, $40 per month for the second line, and $30 per month for each additional line—a family of five would pay $190 per month. Fortunately, you can cancel before then without paying any fees beyond the remaining balance of any financed smartphone.
Additionally, Sprint's pricing is not inclusive of taxes and surcharges, which can cost anywhere from $5 to over $25 extra per month based on our math. These fees typically include a $2.50 administrative charge, 40 cent regulatory charge, state and local taxes, and other regional surcharges if applicable. T-Mobile recently revamped its pricing to include taxes and fees, but AT&T and Verizon do not.
On top of the taxes and surcharges is a $30 activation fee per line, amounting to a one-time charge of $150 for five lines. T-Mobile does not charge activation fees, while AT&T and Verizon charge $25 and $30 per line respectively.
The rest of the fine print is similar to T-Mobile: video streams at up to 480p+ resolution, music streams at up to 500 Kbps, and games stream at up to 2 Mbps. Data de-prioritization applies during times of congestion, and customers that exceed 23GB of data in a billing cycle may be throttled until the next billing cycle. The prices also require electronic billing with AutoPay enabled.
Sprint's pricing is competitive, at least until the promotion expires next year, as seen in the chart below.
T-Mobile's unlimited ONE plan costs $70 per month for the first line, $50 per month for the second line, and $20 per month for each additional line, with taxes and fees included. For comparison, a family of five would pay double—$180—per month. AT&T is even more expensive, since a DirecTV NOW or U-verse subscription is required for unlimited data. Verizon does not offer unlimited data plans.
Sprint said new customers have limited time to sign up to receive the discounted pricing. While five lines are advertised, purchasing one to four lines is allowed—and it doesn't matter if it's family members or friends as long as each person falls under one bill. 5GB of high-speed Mobile Hotspot tethering, VPN, and P2P data is included per month. Tablets can be added for an extra $20 per month per line.
Keep in mind that Sprint ranked last in download speeds and so-called network "availability" among fellow "Big Four" competitors AT&T, Verizon, and T-Mobile in OpenSignal's latest "State of Mobile Networks" report.