T-Mobile is offering another free line to select customers starting today, though figuring out if you’re eligible might take some detective work.

According to The Mobile Report, the carrier has launched a new “Line On Us” promotion called “Loyalty BYOD Dec 2025” that lets qualifying customers add an extra line to their account at no monthly cost. The catch? T-Mobile isn’t being particularly transparent about who qualifies, and the promo isn’t even available through the T-Life app—you’ll need to contact customer support or visit a store to claim it.

These free line offers used to be common during T-Mobile’s “Un-Carrier” era, but they’ve become increasingly rare over the past few years. The last one rolled out in September and only a handful of customers were eligible.

Here’s what we know for sure: You’ll need at least two paid lines on your account to qualify. That’s been the standard requirement for every free line T-Mobile has offered. You’ll also need to bring your own device—financing a phone through T-Mobile on this free line isn’t allowed and could actually cause you to lose the promotion entirely.

There’s also a $35 activation fee to add the line, and if you’re on a plan that doesn’t include taxes and fees (like the newer Experience plans), you’ll still pay monthly taxes on the free line.

Beyond those basics, the eligibility requirements are murky. T-Mobile likely has limits on how many free lines you can already have on your account, but those specifics haven’t been confirmed. The Mobile Report notes that employees can see a special “segment” on eligible accounts labeled “Loyalty BYOD Dec 2025,” but regular customers can’t check this themselves.

If you do qualify, you might see an eligibility notice in the T-Life app or receive a text message about the offer. The promotion started today, so keep an eye on your account if you think you might be eligible.

Source: The Mobile Report