T-Mobile says that nothing is changing for existing customers and the plans that they are on. The company has also said that Go5G plans will remain available for a limited time:
T-Mobile is phasing out plans with included taxes and fees starting [May 1]
By Abdullah Asim, Phone Arena - May 1, 2025
https://www.phonearena.com/news/t-mobile-phasing-out-plans-with-included-taxes-and-fees-tomorrow_id169988