Your message should sound inviting and happy, so the person leaving the message doesn’t get scared off. Don’t be unnaturally over the top happy that they are leaving you a message, but definitely try and get a happy tone into your message, and show them that you value their time and the fact that they are leaving you a message.
Internal Voicemail Greeting Examples: This is used to greet people who call you from within your company (i.e. from another extension). External Voicemail Greeting Examples: This greeting will be played for people who call from outside your company.

From the Skype for Business desktop app (if you are running Click-2-Run build C2R 8201.1002 or later), select Set Up Voice Mail. Change your Call Answering Rules You can change what options your callers have when they reach the voicemail service; get disconnected, hear your greeting, record a message, choose to be transferred to the number or user you select. Change your prompt language This is the prompt language that is played to callers. For list of supported languages, see Languages for voicemail greetings and messages from Skype for Business. Configure your Out of Office greeting This is the customized greeting message that is played to callers when your status is Out of Office. This option can be activated "Always," when you have an active "Auto Reply" in Outlook, or whenever you have an out-of-office calendar appointment.  Where you can get your voicemail messages from
This greeting is heard by a caller once they are forwarded to a voice mailbox. Press the up or down navigation buttons to select Play or Re-Record and then press Enter. Press Enter to stop playback or recording.