I have never tried to, but do you have MAT Worx? If so go to station assignment, put in the ext. number and get the data. Then go to key assignment and select the phone type you are working on, scroll down, and you can change the speaker button to what ever, maybe a speed dial key? or something. As I said I have never tried this but let us know if it works. If it doesn't work you can always go the tried and true method by splitting open the case on the phone and put a piece of electrical tape or equilivent on the circuit board to block the speaker key contact from making a connection. I know that will work!! Been there done that a log time ago with the older NEC 1648 systems that didn't have enough outgoing line/tenent restrictions. Showing my age here!