T-Mobile offers a free additional line promotion

T-Mobile is bringing back its highly sought-after free line deal, but this time around it’s by invitation only. The carrier is quietly rolling out a new “Line On Us” deal to select customers kicking off this month, and while the headline sounds appealing, the fine print and exclusion rules matter more than ever.

What is included with this free additional line offer

This promo will get you an additional line on an existing account for no monthly fee, as long as you qualify and maintain your plan in good standing. There’s a one-time $35 device connection charge to activate the line. If your plan includes taxes and fees in the base price — as do many of T-Mobile’s premium plans — the additional line usually costs $0. If your plan doesn’t include taxes and fees, look for minimal monthly taxes on the “free” line.

It’s strictly BYOD. You’ll need to bring an unlocked phone or activate it with eSIM. Adding financing for a new device on this line is off-limits anyway; that’s a typical limitation T-Mobile bakes into these promos in order to keep costs in check while still showing some loyalty.

Who gets invited to T-Mobile’s free line promotion

T-Mobile is focusing on accounts, not just opening the spigot. Some users are only getting texts, account notifications, or alerts in the T-Life app. Internally, employees can verify eligibility by looking for a “Loyalty BYOD Dec 2025” segment under promo ID ID25079. Customers can ask care or chat support to search for the segment, but only staff members have visibility.

T-Mobile no longer publicly shares the criteria, but previous trends still seem to apply: accounts with at least two paid lines frequently serve as a baseline.

Logically, people who already have multiple free lines (or who snagged a free line earlier in the year) are the least likely to qualify. Those rules can change from one campaign to the next, and that is why this round is presented as targeted rather than universal.

Why T-Mobile runs these recurring free line promotions

Free line promos are not a charity; they are churn insurance. Throw in a free line and it’s harder for families to justify leaving. It also adds new hooks for services associated with that line — something like wearables or hotspots or spare kid handsets — without actually discounting the headline plan price.

T-Mobile has also been the leader in postpaid phone net adds for several years, a fact it highlights during earnings reports and industry analyses. Offers such as “Line On Us” are a silent but crucial piece of that growth strategy. T-Mobile’s withering, dying-on-the-vine demand for BYOD further alleviates its subsidy burden by leveraging T‑Mo’s robust eSIM capabilities and massive 5G footprint that testing companies like Opensignal and Ookla regularly peg among the leaders in availability and speeds.

The fine print that matters for this free line offer

Promotional credits are fragile. Fall below the list price for the required number of paid lines, move to a non-qualifying plan, or migrate your account in certain ways, and the free line credit can go away. That is all it takes to turn a “free” line into one being billed overnight. Before you do, however, check that any plan changes you are considering — such as switching from an older legacy plan to a new tiered account — won’t disqualify the credit.

Just keep in mind the BYOD restriction: you cannot finance a device on the line and continue with the promo. Also, if you are going to finance a phone on the line, select another line to have the installment on and keep this one BYOD. eSIM activation is also usually fast, but you may need an unlocked device that’s eSIM compatible and has a spare slot.

How to check eligibility and redeem the free line offer

Keep an eye out for a text from T-Mobile or an in-app banner within T-Life. If you get nothing, try reaching support and inquire about your account being eligible, as it may qualify; reference promo ID ID25079 and the segment “Loyalty BYOD Dec 2025.” Be sure to have your account PIN handy, verify what the taxes will be on your individual plan, and ask the rep to explain any conditions that may void the promo afterward.

If you do so, have the IMEI or eSIM information for the device you’ll bring along, and be ready to pay the additional $35 connection fee. When the promotion is active, double-check your first two invoices to make sure the promotion credit is being applied properly — sometimes billing systems require a cycle to normalize and it’s far less of a headache catching issues early.

Bottom line: is this targeted free line deal worth it?

This promo can be worthwhile if you already feel T-Mobile is doing right by you and you have a spare phone or a use case (for a tablet, hotspot, or smartwatch) that can use the line whenever needed. That’s less appealing if you were planning to finance a new device on the line or already have several free lines in your account history. As with any “free” wireless deal, the value is real — but only if you fit the rules and will stay put.