Mskanga,
Actually,
that used to annoy me too. However, now one of the areas I am responsible for is a call center. We actually DO use those calls, mainly for retraining after a customer has complained about a particular agent and the way they were dealt with. We work with the agent on techniques for handling this type of call again.
Also, once in a while, more information is needed, and can be gotten by going back to the original call.
But you know, if you are going to be involved in a business cal you want a record of, using your answering machine isa great way to do so.
Hope this helps explain the reason for the annoyance.