You can trick the caller with funny jokes before the actual greeting message beeps. Keep such kind of voicemails for close friends and family members. They will find it amusing soon after making the call. The machine says Hello, not Me. So respond to what the mechanical device orders you. Play the game of in and out to find me out! Listen to the voice after the beep. Yes yes yes, we are not yet in and we do not want to bore you with a long voicemail text. Leave your message after the beep. I cannot lend my ear so I have kept the machine as my assistant. Record. I love your voice! I want to hear you. Speak up to record.
Pro Tip: Smile while you’re recording your greeting and your voice will sound pleasant.

Context does matter here. If the caller would reasonably expect you to answer the phone (such as if they were calling a store or other place of business), an apology for not being able to get to the phone makes the most sense.
When you create a professional voicemail greeting, it can be a good idea to think about what your callers might want to know. After doing so, you can make a list of points to cover in your voice message; it might also be a good idea to write out the entire greeting on a piece of paper. The ideal message should be somewhere between 10 and 20 seconds, so you may want to time yourself repeating your message before you record it. After composing your telephone message, it can be a good idea to get a second opinion of this greeting so you can make sure it sounds professional. Writing down a voicemail greeting helps prevent mistakes when recording it.