Samsung Galaxy Note5 User Manual page 119

Setting
International dialing
DTMF tones
Voicemail settings
For more information about Call settings, see Phone Settings.
Phone App
Enter the international dialing code automatically (only when US
dialing is disabled).
Set the length of DTMF tones, which are used when pressing the
keypad while on a call.
Configure your voicemail.
Description
109