In order to achieve true "hold button" activation, we created a small module called a TEHMA (telephone extension hold music activator). This line-powered activator sends a signal down the phone line telling the MOH 500e unit whether or not the phone is on hold. Only phone extensions with a TEHMA can put a call on hold with the phone's hold button. Extensions without a TEHMA can put a call on-hold py pressing the key twice.