If voice mail options are grayed out, you're using the Skype for Business voice mail service with cloud PSTN. Voice mail options aren't available in Outlook.
Note: The text messaging notifications feature is only supported in specific regions and for specific mobile service providers. If you don't see your mobile service provider listed, you won't be able to set up text messaging notifications.

Set the number of rings you'd like callers to hear before they hear your voicemail greeting.
When you receive a voicemail, a notification will alert you on Skype for Business apps, desktop phone, and email app. If the caller hangs-up before leaving a message, you will receive a Missed-Call Notification email with the caller information (if it was not blocked). What's it like for callers to leave messages? Depending on the users settings for Call Answering Rules Callers can hear a greeting, record a message (up to 5 minutes), and/or choose to be transferred to the target defined by the user. Visit your User Settings Portal https://aka.ms/vmsettings to learn more. Repeat menu All of the menu prompts will be repeated for callers so if they don't press a key on their phone before hanging-up, the menu prompt will be repeated three times. Thank you! Any more feedback? (The more you tell us the more we can help.) Can you help us improve? (The more you tell us the more we can help.) Resolved my issue Clear instructions Easy to follow No jargon Pictures helped Other Didn't match my screen Incorrect instructions Too technical Not enough information Not enough pictures English (United States) Sitemap Contact Microsoft Privacy Manage cookies Terms of use Trademarks Safety & eco About our ads © Microsoft 2021 Open the Phone app . Press and hold “1” to call your voicemail. Enter your PIN and press “#”. Press “*” for the menu. Press “4” to change settings. Press “1” to change your greeting. Follow the recorded instructions. How do I change my voicemail message? From the Home screen, tap the Phone icon . Tap Voicemail then tap Greeting (upper-left). Greeting is located in the top-left corner of screen. Tap Custom to record a greeting. Enabled when a checkmark is present. Tap Record to begin recording the custom greeting message. Tap Stop to end recording then tap Save. Call *86 (*VM) from the handset or the 10-digit mobile number from another phone. Follow the instructions for choosing the language options then press the # key to confirm the choice. When prompted, enter the 4-7digit password then press the # key. When prompted, say the signature (or name) then press the # key. Open your Android’s Phone app. It usually looks like a phone receiver at the bottom of the home screen. Press and hold the 1 key on the keypad. Tap Add number. Tap Service. Tap My carrier. Tap Setup. Tap Voicemail number. Type your mobile phone number and tap OK.