Yealink SIP-T2XP Administrator's Manual page 267

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Do one of the following:
Ensure that the configuration is set correctly.

Reboot the IP phone. Some configurations require a reboot to take effect.
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Ensure that the configuration is applicable to the IP phone model.
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The configuration may depend on support from a server.
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They are codes that the IP phone sends to the server when a certain action takes place.
On code is used to activate a feature on the server side, while off code is used to
deactivate a feature on the server side.
For example, if you set the Always Forward on code to be *78 (may vary on different
servers), and the target number to be 201. When you enable Always Forward on the IP
phone, the IP phone sends *78201 to the server, and then the server will enable Always
Forward feature on the server side, hence being able to get the right status of the
extension.
Do one of the following:
Reset another available IP address for the IP phone.

Check network configuration via phone user interface at the path

Menu->Settings->Advanced Settings->Network->WAN Port->IPv4. If Static IP
Client is selected, select DHCP IP Client instead.
Reset your phone to factory configurations after you have tried all troubleshooting
suggestions but do not solve the problem. Note that all custom settings will be
overwritten after resetting.
To reset the IP phone via web user interface:
1. Click on Settings->Upgrade.
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Troubleshooting
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