AASTRA 4187 Plus for BusinessPhone User Guide EN - Manual (Page 65)

65 BusinessPhone – Dialog 4187 Plus
Other Useful Features
DTMF Tones
The DTMF function – also known as Suffix Dialling – is used to
control answering machines or any other telecommunication
devices. u
Lift the handset.
z
Make an internal or external call to reach the desired device.
When your call is answered you can continue to dial digits which
will be sent as DTMF digits (tone signals) to the called device in
order to activate the desired functions.