I provide my cell phone number as a direct contact to most of my clients and other important people. I would prefer that a client call me directly rather than take up my secretaries time, who then has to transfer the call. If I am not available, the message hits my voicemail inbox. Again, my secretaries time has not been affected by routine telephone maintenance.
We try and train clients to call the right person at my office depending on what their issue involves. So far, it has worked great.