I have never done it, but have you ever went into centralized programming and tried to see if you can program a button in a single line phone? It sounds crazy, and I have never tried it, but if you go into centralized programming on an MLX-10D phone, you notice that you have about 28 buttons to program even though your phone only has 10. If you went into Centralized Programming for the single line set, and could program a button as a System Access, then go into Voice Announce, and define that button to place voice calls, that may work. You would always have to voice announce on internal calls which may be a bad thing. But it is an option to try. Good Luck