Here's the one that i wanted to have, back when I worked in a certain office...
"Hello, you have reached [Office name].
We are unable to answer your call at this time.
Please leave a message at the sound of the BLEEP, and we will return your call at your earliest inconvenience.
Thank You!"
All of us in that office were suspected of being up to something (our bosses weren't stupid!), and eventually, a pre-recorded message was placed on the phone system. A sensible precaution!
Tom