the fixed system message, "I'm sorry, the person you are calling is currently on the phone." followed by the fixed system prompt, "Begin speaking after the tone, then hang-up when you are finished or press any key for further options."
Good voicemail messaging can help, but a great receptionist can convert leads far better We understand that you’re not always able to get to the phone. More and more, we’re turning to text and voice messages, too — you know, the little microphone down there at the bottom of your message screen that records what you would typically text.

There is no definitive answer here, but you should include one of the two at the beginning of your message based on what makes the most sense.
Typically, most of these services are uniform—i.e. include the same tools and features (send a script, they record it in a tone you approve, they send it as a file, you supply any feedback, etc.); however, there are some services that go above and beyond. For example, VoiceOverPro, is a single voice professional who records 30 second voicemail messages based on users’ scripts. This is standard; however, users also have options like adding music, recording up to 60 seconds (or 150 words), rush, 2-day turnaround, and even same day delivery.