Need to silence ringing volume on a Bellsouth MH9111

I would like to know if there is a way to silence the ringing on my current cordless telephone or if there is an existing model with the featured capability of silencing the ring tone.

I am using a Bellsouth 900MHZ Model MH9111 cordless telephone as an extension phone (from my message center answering/fax device) in a small office environment. I am able to silence the ringing on the answering device but unable to silence the ringing on the cordless extension phone that has a volume control that permits only the options of low, medor high). Ringing at the low range still presents a distraction in my consulting sessions.