From the Customer Portal refer to DID Numbers -> Voicemail, then you will see the following screen. In there you will be able to see a list of any existing Voicemail accounts, or create a new Voicemail account (Mailbox) by clicking on the "Create New Voicemail Account" Button.
The best after hours greetings are brief, direct, and punctual. Do not waste the customer's time and give them a reason to hang up by adding in unnecessary details. The information in your after hours greeting should remain concise and essential to the caller's needs.

Of course, we want to know as soon as an incoming voicemail is saved, so again, it’s Twilio to the rescue. By adding a few lines of code to our Python script, Stacey and I each get an SMS notification telling us there’s a new message. Note that Twilio’s API requires a separate call for each message to be sent, which is why the similar code repeats once for Stacey’s phone number and then again for mine. If you plan to send bulk messages from Twilio, I expect that you can build a list of phone numbers and loop through them with the API call. Since we only have two contact numbers and don’t expect to add any more, I decided not to loop through a list of two elements.
Visual voicemail on a Skype for Business desktop phone, Skype for Business app, or the Lync client for Mac.