The new terms will be applicable from July 1st, meaning devices purchased on a promo before July 1st will not be subject to the new stipulations.
Most customers are going to be annoyed at the new change and it could prove to be the last straw for those who are already considering leaving the company because of the recent price hike.
T-Mobile might have made the change to deter customers from selling devices they purchase via promos. The company committed to a new phone unlocking policy for Mint Mobile and Ultra Mobile customers to get the acquisition deal approved and its own customers are only required to use their devices on the network for 40 days before they are eligible for unlocking. The new change could be a way to restrict customers despite the generous unlocking policies and stop them from purchasing and selling devices.
Another motive could be to encourage people to move to the Go5G Next plan, which allows for yearly device upgrades.