Final answer:
The price of T-Mobile ONE for a family of 4 starts at $140 per month.
Step-by-step explanation:
The price of T-Mobile ONE for a family of 4 will depend on the specific plan and options chosen. T-Mobile ONE offers unlimited talk, text, and data for each line in the family plan. As of my knowledge, the starting price for T-Mobile ONE for a family of 4 is $140 per month (as of September 2021).