Oh - if anyone is still curious: I recorded the greeting via the phones custom greeting function, then called to listen to it from another phone, then turned off the phone and called again. Same message. I had wondered if just maybe the phone played the message when on, and the carrier played the message when the phone was unreachable.
Open Phone → Make sure you are on Keypad → Press and hold the number 1 for a few seconds. It will call your voicemail; You can check your voicemails here. 3. Force close and reopen the Phone app. To force close Phone, on iPhone X and later swipe up until you see the apps in task view, then swipe up again on Phone.

7. T-Mobile Visual Voicemail. Not all people actively use voice mail. In case you have to use it sometimes, you can download T-Mobile Visual Voicemail – it allows you to send infrequent voice mail messages.
Company-level calls are usually directed to your general business number. There are occasions when everyone in the office is tied up and unable to pick up calls. It’s important to gather information about the reason for the call so that the right person or team can call them back. These greetings ensure that customers do not feel neglected while also providing assurance that their call will be attended to as soon as possible.