Sony IT-M10 - Manual (Page 8)

Speed dialing
You can store the numbers you frequently call into the memory of the
phone so that you can dial a number with the touch of two buttons.
Storing speed dialing numbers
You can store up to 10 speed dialing numbers. These 10 numbers are
stored commonly for both line 1 and 2 so that you can use them on both
lines.
1
2
3
4
5
6
Press either (LINE 1 ) or (LINE 2 ).
Pick up the handset.
Press CPGM) (program).
Dial the phone number you wish to store.
You can enter up to 16 digits for pulse dialing or 15 digits for tone
dialing. Note that tone and pause are each counted as one digit.
Press ( SPEED dial ) and the desired dialing key (0 to 9).
Replace the handset in the cradle.