A friend of mine has a recording facility for his telephone calls from the company. He was getting concerned that calls containing disputed items were mysteriously being "mislaid" by his company. He also records all calls from his company mobile phone using a pocket recorder.
He advised the company that all calls pertaining to company business would be recorded.
Surprise, surprise, he doesn't get any threatening phone calls and everyone is sweetness itself when talking to him.
You can always advise that calls MAY be recorded and enjoy the attitude change.
It works!
BTM