VTech 15100 User Manual page 23

Steady when more characters are existed before the text
currently displayed.
Steady when more characters are existed after the text
currently displayed.
Press to select more menu options if applicable
(MENU)
Press to confirm the current selection if applicable.
Press to initial an intercom call when idle.
(INT)
Press to go back to previous menu level or cancel the
current action if applicable.
(BACK)
Press to clear a character or stop the alarm if applicable,
press to mute / unmute during a call.
Steady when when you have received missed calls.