I would say there are 3 types of voicemail:  Nothing voicemail, something voicemail, and cryptic voicemail. 

Nothing voicemail sounds like this:  "Hey, I was just calling to see what's up.  Give me a call back sometime if you get a chance."  With this kind of voicemail, the intentions are clear ("see what's up"), a response is optional ("if"), and the time frame is relaxed ("sometime"). 

Something voicemail sounds like this:  "Hi, I have a question about XYZ.  Give me a call back when you get a chance."  In this case, the intentions are clear ("question about XYZ"), a response is recommended ("when"), and the time frame is somewhere between relaxed and urgent ("when you get a chance"). 

Cryptic voicemail sounds like this:  "Hello, I have something important to talk to you about.  Call me back sometime today.  I'll be up till midnight."  This time the intentions are quite unclear ("something important"), a response is critical, and the time frame is immediate ("today ... till midnight").  This is the kind of voicemail I got from my dad last week (sorry Dad, I couldn't let this go).  When you hear a voicemail like this, thoughts go immediately downhill.  Did someone die?  Did someone's house burn down?  Did an alien abduct my sister's baby?  Any of these things are possibilities with a message like this.  If it wasn't an important thing, I wouldn't need to call back in such a specific time frame.  If it wasn't all that serious, you would've just said what you wanted to say.  But since you left out major important details and basically gave me an ultimatum, I was forced to fill in the blanks, and that didn't go so well. 

The problem with cryptic voicemail is that Wendy and I get at least one per week from her mom.  Every message goes something like this:  "Hi, Wendy?  It's mommy.  I need to talk to you about something.  Call me back as soon as you can."  Wendy comes from an interesting family where bad stuff happens all the time.  Somebody dies or loses their job or gets in a car accident all the time.  So getting a cryptic message like that is a little unsettling.  Wendy usually goes through a list of possibilities, all of which cause an unhealthy amount of stress, worry, and stomach pain.  But when Wendy calls back, her mom usually says something about her cat throwing up on the couch or her senior citizen neighbor making advances towards her.  While these are significant events, they don't warrant the use of a cryptic voicemail. #technology