Why can't I save custom voicemail messages?

One thing I've never understood about the iPhone is that despite the simplicity of recording and uploading a new voicemail greeting, the phone does not allow you to SAVE your old greetings for future use. I have a lengthy VM greeting introducing my business and giving callers options about how to reach me, as well as a healthy mistrust of my own performance. When I go on vacation, I change the message to reflect that. But when I come home, I would love to go back to my "best" voicemail recording rather than having to record a new one every time. Is there some way to do this?