how can I reset my Southwestern Bell Freedom Phone?

Model FS 900 - Executive Key Telephone Set
At my location - the function keys (hold, redial, etc.) stopped working. If relocated to another phone jack this phone works perfectly. When another phone (in perfect working order) is plugged into my station - the function keys (hold, redial, etc.) stop working. I heard there is a series of codes I can input into the phone to test/reset and hopefully clear the malfunction - the AT&T phone guy checked the phone lines - said all is well.