Aastra Telecom SIP 480I - Manual (Page 258)

Advanced Operational Features
6-10 41-001129-00 Rev 09, Release 1.4.1
IP Phone Administrator Guide
Advanced Operational Features
Aastra Web UI
Step Action
1 Click on Advanced Settings->Global SIP->RTP Settings.
2 Enable the "Two Call Support" field by checking the check box.
(Disable this field by unchecking the box).
3 Click to save your settings.
Note: The session prompts you to restart the IP phone to apply the configuration settings.
4 Select Operation->Reset and click ..