AT&T MERLIN LEGEND MLX-10 Non-Display Telephone User Manual page 23

Your MLX-10 Telephone
ICOM Originate Only. Use this button to make inside calls;
calls do not come in on this button. This button is set up by
your company to make either inside ringing or voice-
announced calls.
555-1234. Use any button labeled with a phone number to
make or receive outside calls only. This is called a "personal
line" because it appears only on your phone or on a particular
group of phones.
WATS. Use buttons labeled with special service names like
WATS to make and receive outside calls at a reduced cost.
1-10
Line Buttons