AT&T Merlin II Release 3 System Manual page 17

The 34-Button phone has two columns of five buttons above the dial pad for
outside lines, intercom, and programmable features. This phone also has two
columns of 12 buttons to the-right of the dial pad for Auto Intercom buttons
and other programmable features that do not require lights. See Figure 2-10.
The 34-Button Deluxe phone is like the 34-Button phone except that the 24
buttons to the right of the dial pad have two lights per button that can be
used for Auto Intercom buttons and other programmable features requiring
lights. See Figure 2-10.
34-Button phone 34-Button Deluxe phone
FIGURE 2-10 34-Button and 34-Button Deluxe phones.
HFAI-10, SP-34, and SP-34D Phones
Each of these models has a built-in speaker that allows you to answer and
make intercom calls without lifting the handset.
The HFAI-10 phone has two columns of five buttons located above the dial
pad for outside lines, intercom, and programmable features. See Figure 2-11.
HFAI-10 phone
FIGURE 2-11 A HFAI-10 phone.
MERLIN II System Telephones 2-9