T-Mobile is offering new and existing customers a FREE line of service for a limited time. To qualifying, existing customers must have 2 or more lines and for new customers, they must add 2 lines with the 3rd being Free. For existing customers, you must be on one of their qualifying plans to get this offer. Those plans including Simple Choice, ONE, and Magenta. Exclusions will apply, including discounted plans (military, first responder, and 55+) not being eligible. Also, not all Simple Choice plans qualify. Taxes and fees may apply depending on your existing plan. This may include a SIM or activation fee, which could be possibly be waived later. To get this offer, contact T-Mobile customer support online (through their app, texting 611 on a T-Mobile phone, T-Force FB Messenger or Twitter) or through the phone and ask if your plan qualifies. The reference code for this offer 20Q32# but you can also mention the larger banner ad that’s on T-Mobiles front page right now. The Free line will be provided in the form of monthly bill credits and they will end if you cancel any lines.

Source: Reddit