Go to the website of AceThinker Online Audio Recorder, and click on the "Start Recording" button from its main page. For starters, click on the "Open Apowersoft Online Launcher" button to launch the audio recorder. Next, plug one end of your audio cable to your computer's microphone jack and the other end to your phone's audio jack to connect both devices.
Your voicemail should be very specific. It should be short and urgent. Use word's like "need", "should", "must" , or "have to" to create a sense of urgency. For example, say something like, "We need to discuss..." or "We should talk about..."

Hello, it’s obvious you have bad timing, because nobody is home. Please leave your name, telephone number, and a brief message in a voice similar to mine, and your call will be returned as soon as humanly possible.
Additionally, you will want to close out your voicemail by (re)stating your contact information and name and purpose of your call. This is another little trick of leaving voicemails - people tend to remember the first and last things you say more so than the middle, so by summarizing the important pieces of your message at the end, what you said is more likely to stick.