Update 3/12/23: Looks like this is available again.
The Offer
Direct link to offer
T-Mobile is offering postpaid customers with two or more lines an additional free line (must pay $35 line activation fee and line isn’t eligible for any free phone promotions). To get the line added you must message T-Force on Twitter/Facebook. Promo is ‘2022 BYOD Line P1’. Eligible plans include:
Simple Choice Plans
Magenta Max
T-Mobile One
Our Verdict
Looks like you need to also have been a customer for at least 12 months and be a T-Mobile customer rather than Sprint to be eligible.
Hat tip to Slickdeals & @Louie_tweet