AT&T TL74308 - Manual (Page 9)

4
Getting started
Additional handsets (optional)
Add new handsets to make your telephone more versatile (see page 68)
Your telephone can accommodate up to four cordless handsets. You can add
new handsets (model TL77008, sold separately) anytime, but each must be
registered with the telephone base before use.
The handset provided with your TL74108 is automatically registered as
handset 1. You can register three additional handsets. Additional handsets will
be assigned numbers in the order they are registered (handset 2, handset 3,
and handset 4).
The TL74208/TL74258 has two handsets automatically registered as handset
1 and handset 2. You can register two additional handsets, which will be
assigned as handset 3 and handset 4.
The TL74308/TL74358 has three handsets automatically registered as
handset 1, handset 2 and handset 3. You can register one additional handset,
which will be assigned as handset 4.
The TL74408/TL74458 has four pre-registered handsets, so you cannot
register any additional handset to it.
NOTE: All four handsets can be used simultaneously, however only two handsets can be
used on an outside call, while the other two handsets can be used on an intercom call at
the same time.
Handset 1 Handset 2 Handset 3 Handset 4