You could always change your answering machine message to feature your voice shouting "Hello? Hello? I can't hear you! There's too much wind! Hello? <click>" with a lot of wind / static noise in the background. Then, just don't answer the phone.

Be sure to change the message back afterwards, though, or your customers will be suspicious.
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Paul Grzelak
200GB with 48MB RAM, Illuminated Buttons and Digital Outputs