This T-mobile doc has more on the 6-15 digit "PIN/passcode": https://support.t-mobile.com/docs/DOC-37477 Note that it can be set up via the T-Mobile web sit

This T-mobile doc has more on the 6-15 digit "PIN/passcode": https://support.t-mobile.com/docs/DOC-37477 Note that it can be set up via the T-Mobile web site, alternative to the phone support line.