I was having the same trouble with mine! (Your talking about the desktop answering machines right?)
Excuse me while I zero in the scope!
Well I happened to get a call from my local telephone company offering a package that included a voice mail service so, I thought I would give it shot. It took two weeks before I got around to setting it up and after I did I figured it was 2 weeks too late. It had messages on it before I even put a greeting on it.
(Had too eat some crow with a few regular customers) It works great!!!!!!! I also have the option to forward my calls to any number I want. When I know I will be out all day I forward them to my cell. Since I pretty much do most things by myself forwarding the phone makes me more accessable. And if I can't answer the cell it also roles over to voice mail.