Listen to your messages and return your calls as soon as possible. Of all the lines of communication available (social media, text, email, etc.,) your callers resulted in picking up the phone to call you because they wanted to speak with a live person. Do them the common courtesy and give them a call back when you first have the chance.
Voicemail transcription (beta; available only in certain countries or regions) shows your messages transcribed into text. Transcription is limited to voicemails in English received on your iPhone with iOS 10 or later. Transcription depends on the quality of the recording.

Here are some helpful links to help you record voicemail greeting that is clear and professional. Record your phrases for recording a great voicemail greeting here. Record yourself and compare it with a native speaker. Hear Georgie giving helpful feedback to other students on their voicemail greetings.
There are many little things I instinctively look for and notice and one of them is a person’s voicemail greeting. I often conduct initial phone interviews and when someone’s personal voicemail greeting turns me off, the interview process is over. It’s their first and last impression.