Sources: https://old.reddit.com/r/tmobile/comments/174uelk/megathread_forced_plan_migration_for_older_plans/
https://ibb.co/dJcyMNm
T-Mobile is planning to force customers on the following plans to newer plans unless you opt out:
(migration paths per plan in sources above)
Customers can opt out by contacting support after October 17th. Notifications will begin going out on that date via email and SMS.
The changes are set to take effect in November.
Free lines on your account will likely stay free. Free lines have migrated easily in the past and that is expected here as well. The only time free lines turn to paid lines is when migrating to Go5G Next (+$10 for each free line), which none of these forced migrations do.
