shabbos phone

am completing my training in Internal Medicine in New York and will be joining a practice in which I will likely have to occasionally take beeper-call on Shabbos which will force me to use the telephone to return messages.

I have unsuccessful in tracking down a shabbos phone developed by the machon in eretz Yisroel. I would very much like to purchase such a phone (and perhaps multiple phones). Perhaps you can help.

Also, I was wondering if there is any written material that explains how the phone works, which poskim have sanctioned or encouraged its use, and what the advantages are over a traditional phone.

thank you very much