Aastra Telecom SISIP 57I CT - Manual (Page 166)

Operational Features
5-38 41-001160-00, Rev 01 Release 2.0
IP Phone Administrator Guide
Operational IP Phone Features
Aastra Web UI
1 Click on Basic Settings->Preferences->General.
2 Enable the "Suppress DTMF Playback" field by checking the check box.
(Disable this field by unchecking the box). Default is disabled.
3 Click to save your settings.
You must restart your IP phone for the changes to take affect.
4 Click on Operation->Reset.
5 In the "Restart Phone" field click to restart the IP phone and apply the changes.