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The issue is currently under investigation.
Configuration
When these handsets download their configuration, they do not clear or reset any settings that are not explicitly contained in the config file. As an example of this behaviour (how we noticed it), when a handset is first configured for multiple lines (ie. 2 different sip accounts), then later, if one of the lines is removed from the SipXecs interface, it is never removed from the GXP-2000. This is because the configuration for the second line is simply removed from the configuration, as opposed to being overwritten or reset to default values. This can be handy, if new settings are introduced in firmware updates, but which are not yet supported in the device template on SipXecs. In this case, the settings can at-least be set manually, and will not be overwritten by the downloaded config.
Useful Details
Phonebook
The 'phonebook' on the handset is limited to 349 entries in the current firmware revision. Entries in the phonebook override 'caller-id name' for incoming calls, and are responsible for outgoing 'called name' lookup. The phonebook can be either manually entered on the handset, or downloaded from a server. The file 'gs_phonebook.xml' will be downloaded from the configured server, which can be hosted via HTTP or TFTP.
The configuration screens on the phone allude to an 'LDAP' phonebook. This is a serious misnomer, as it has nothing whatsoever to do with LDAP. Instead, if configured, the phone makes an HTTP call to a script (could be php, .cgi, etc) which is expected to return the phonebook results in the same .xml format as is used for the 'gs_phonebook.xml'. This script CAN be passed parameters, which it should use to limit the returned results. Unfortunately, the 'LDAP phonebook' is NOT used for the 'called name lookup' or the incoming caller-id override as described above.
Configuration
The GXP-2000 handset hosts a web configuration interface. This can be handy to view the current settings of the handset, but if the phone is configured to download it's configuration from the server, and is provisioned in SipXecs, any changes made via the Handset's web interface will be overwritten upon reboot. This is further enforced by the fact that ANY change to the handset settings via the phone's web interface requires a reboot to take effect.
A utility called 'gsutil' can be used to dump a plaintext decoded version of the configuration from the handsets. This utility is available from http://www.pkts.ca/gsutil.shtml. This can be particularly handy when trying to compare configurations.