"When, and if, it launches its 5G network on December 6th, T-Mobile will offer a new $15 per month prepaid 5G plan to customers. The plan will include a 2GB per month data allowance, in addition to unlimited talk and text. At $15, the plan is half the price of T-Mobile's current cheapest plan. For $25 per month, customers can upgrade to a plan with 5GB of monthly data. Additionally, T-Mobile says it will add 500MB of data to both plans every year for up to five years." - Engadget
For more Data, the rep that I spoke with said that 6GB will cost $25 and there will be a 10GB plan (if I remember correctly for $30).