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.
Insurance agents have to deal with large numbers of clients almost all through the year. So, they are extremely busy and cannot take calls of clients. For them resorting to voicemail messages become inevitable. Here is one instance of VOIP phone service for businesses like this:

These voicemail ideas may not come so easily for some of you. And who says that finding inspiration is a bad thing. It’s natural; not everyone has a funny bone inside them. But that doesn’t mean you get stuck with a boring, cliché greeting. It has to be different and contain some kind of style. And to that, I would like to give you a list of messages. They are perfect alternatives when you want to add some uniqueness to your voicemail. These cool voicemail ideas given below will take the mundane effects off and leave you with fresh sounding voicemail messages. So take a look at some funny greetings that you can use as your funny cell phone voicemail ideas (or home phone).
Your phone number is the last thing you should say on a voicemail. Say it once, slowly, and make sure to repeat it again. This has two benefits: First, it makes your phone number the last thing they hear, which encourages an immediate callback.