On Android devices above Android 5 (Lollipop), open the Phone app. Then, press and hold "1" to call your voicemail. Now, enter your PIN and press "#". Press "*" for the menu. Press "4" to change settings. Press "1" to change your greeting. Make sure to follow all the instructions.
If this does not successfully link you to your voicemail account, follow the steps outlined below. Press the three dots on your keyboard (upper right corner of the screen)Select “Settings” from the drop-down menu.Select “voicemail” from the drop-down menu.Select “Advanced settings” from the drop-down menu.“Setup” should be selected.Click on the “voicemail number” option.Enter your ten-digit phone number and press the “OK” button.To return to the main menu, press the home button. Obtaining Access to Your Twigby Voicemail from a Different Phone:

If you are recording a voicemail message for business, be sure you include your name and your company’s name, so people know who they are calling and were they are reaching them. If you do not include the business name, they may think they have mistakenly called you at your personal number. Step One: Introduction. Start with an upbeat greeting that includes the name of the person you’re calling: “Hi, Tim!” “Hello, Susan!” “Good morning, Tom!” Then, introduce yourself by giving your name, company name if applicable, and telephone number. Step Two: Message. Step Three: Recap and sign off. What is a professional voicemail greeting?
4. Setting Up a T-Mobile Voicemail: Open your iPhone's Phone app. It's the white phone icon on a green background on the Home screen. Tap "Keypad". It's one of the options at the bottom of the screen.