What does it mean to whitelist a number?
To whitelist a number means to add a phone number to a list of “approved” contacts that are allowed to reach you without being blocked, filtered, or flagged as spam. It's the opposite of blocking a number.
How to whitelist a number with T-mobile
Launch the T-Mobile 'T-Life' app and click 'manage'
Scroll down and tap Scam Shield
Tap into “Allow calls”
Check if the Nagish or Regular number is listed in red for 'scam likely' (See: What is my Nagish number)
Select the number or numbers and tap 'calls allowed'
Go back to 'Lists'
Tap 'Allowed numbers' to confirm the numbers you've allowed are listed
Tap 'Blocked numbers' and 'Send directly to voicemail' to ensure that callers you want to receive calls from are not listed