Your greeting is very important as it can be the first contact people have with you or your company. Voice mail is only impersonal if you make it that way. One way to help increase the effectiveness of voice mail is to change your greeting at least weekly if not daily.
Your greeting should let the caller know who they have reached, what is the persons status ( out of the office, in the office but in meetings etc), when the caller can expect to receive a call back and instructions on what to do if the call is urgent.
Here are a few sample voice mail greetings: