AT&T Merlin Legend 10BS User Manual page 41

Your Analog Multiline 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 a
specific group of phones. It is a direct outside line that does
not need a dial-out code.
1-26
Line Buttons