Credit: Joe Maring / Android AuthorityTL;DRT-Mobile is offering you the chance to add one paid line and get a second for free.To qualify, you’ll need two existing paid lines in addition to the two lines added by the BOGO offer.You’ll need to select a mid-range plan like Experience More and keep both the paid and free lines for at least a year.All three of the big carriers will occasionally run special offers for free lines, though Verizon and T-Mobile engage in this practice way more regularly than AT&T does. T-Mobile takes the most aggressive approach here, regularly offering BOGO promotions that will let users add one paid line and get a second line for free.As first spotted on Reddit, the latest T-Mobile BOGO offer is up. These two-for-one deals are particularly great for families that are considering adding their kids.