For clarity's sake: T-Mobile isn't starting its own bank. Instead, it's handing the financial duties over to mobile-first banking institution BankMobile, a division of Customers Bank. T-Mobile Money will operate like your standard checking account. You'll get a Mastercard debit card, a mobile app to manage your money directly and FDIC insurance on balances up to $250,000. Your T-Mobile Money card will also be compatible with NFC payment services like Apple Pay, Samsung Pay and Google Pay.
What makes T-Mobile Money inticing, at least for current T-Mobile subscribers, is the promise of four percent APY (annual percent yield) on your account balance. There are some catches with that sweetener, though. The four percent APY only applies to balances up to $3,000 (you'll get one percent APY on everything above that) and you'll have to deposit at least $200 per month into the account. T-Mobile is also offering other perks including $50 overdraft protection, but again, you'll have to meet that required minimum deposit to get it.
If you're not worried about optimizing your APY, you can use T-Mobile Money as a standard checking account. There are no account fees, no maintenance fees and no minimum balance required to keep your account open. You'll also have access to 55,000 no-fee ATMs through the Allpoint network.
T-Mobile has been down this road before. The company launched Mobile Money, a service aimed at people who couldn't get traditional checking accounts, back in 2014. It was shuttered in 2016.