You can receive incoming calls, but are unable to make any outbound calls on a Grandstream branded handset.
The handset will display an error "No Response" when you attempt to make a call.
By default, Grandstream phones add a number of additional SIP headers which can cause issues in initiating outbound calls.
In order to fix the problem, you'll need to disable a number of "Custom SIP Header" options in the phone's configuration.
1. Log in to the phone's web interface
2. Navigate to Accounts > Account 1 > SIP > Custom SIP Headers
3. Set the following options to "No"...
4. Click the "Save and Apply" button
5. Reboot the handset
6. Make a test call to confirm the issue is resolved
Should this not resolve the problem, please Contact Us for further assistance.