On the Phone tab, click the voicemail icon below the dial pad, and then click Change Greetings. Skype for Business calls your voicemail and guides you to record a personal greeting. When asked to press a number, pause on the phone/mic icon and click a number under the DIAL PAD tab.
For each assigned function, enter additional information or phone numbers and extensions to transfer calls. Edit a Greeting for a Business Hours Auto Attendant

No one wants to sit and listen to someone talking drone and monotone on a voicemail greeting. Remember to keep it upbeat and avoid sounding like a robot!
Humor also leaves a lot of room for misinterpretation—which subsequently weakens sincerity and authority. A caller can be very turned off by merely misinterpreting your joke. Why take this risk? Additionally, this could even cause callers to question your character. Say, for example, the president of a company’s mobile phone voicemail greeting was funny. What’s to happen if the caller didn’t like or get the joke? What if they found it offensive? Another scenario is that a caller is reaching out to you for the first time—i.e. they have no idea regarding your personality. What next? The point is, with this type of greeting, humor is bound to be more divisive so just avoid it altogether. c. Poorly Pacing Your Message and Bad Time Management: Don’t speed through your message. Speak clearly so callers know what to include in their message and when to leave the message. At the same time, don’t drag your message out. No one wants to sit through a diatribe. Just get to the point clearly.