By default, iMazing will export all the voicemail from the selected contact(s). If you only want to export specific voicemail, select them now. In the bottom toolbar, click Export. This will open a save panel dialog box. In the dialog box, select where you want to export your files, then click Choose. Use the CTRL/Command or SHIFT keys to select multiple contacts or voicemail. Double-click your voicemail to preview it. Transcript column
Hello, you have reached X (service provider). Unfortunately, all our agents are engaged in talking to other customers. You can stay online or to resolve something urgent, try our live chat service. You also have the option of leaving your name, ID and number and our agents will revert to you at the earliest.

If you create a call answering rule but don't specify an action, your caller will hear the following prompt: "You have reached the mailbox of . Please call back later. Goodbye." and the call will end.
You might also consider giving them the option to skip your voicemail message completely by pressing another key (again, check with IT). You also want to make callers aware what you will return their call, instead of telling them that you will try to return their call--and let them know when you are likely to do it, if possible. If necessary, provide additional or emergency information in your voicemail greetings. My dentist, for example, lists his cell phone number for emergencies.