AT&T 2255 - Manual (Page 12)

Set Dial Mode
NOTE: When you change the dial mode setting, BOTH handsets are
affected.
This phone comes set for touch tone ( DTMF) dialing. If you have dial pulse
(rotary) service, set the dial mode to PULSE.
1 Press
S.
2 Press < until the screen displays
3 Press
S. The screen displays
4 Press < or > to display DTMF or PULSE.
5 Press
S to save displayed setting.
10
FEATURE SETUP
>DIAL METHOD
CALL LOG
>DIAL METHOD
DTMF