T-Mobile is giving away 4GB of High speed data instead of regular FREE 2.5GB High speed data.
You can login into your account, click "change data" under the plan you will see 4GB for 0.00. Change from 2GB to 4GB and Submit. You will see a message "you will have 4GB data until 02.28.2019 and then 2.5GB"
I hope it is not YMMV