http://www.grandstream.com/index.php/support/tools

Only the latest firmware 1.0.3.37 supports DHCP VLAN discovery.

The latest firmware 1.0.3.37 does not seem to be compatible with the current commercial FreePBX EPM.

Grandstream phones auto-reboot endlessly if they don't like the configuration files.

Try performing a factory reset if you experience provisioning problems.

Perform a factory reset after any firmware update.

This is a 'normal' phone reboot:

[root@ppmpbx ~]# tail -f /var/log/messages
Aug 23 13:51:38 ppmpbx in.tftpd[21710]: RRQ from 192.168.71.68 filename cfg.xml
Aug 23 13:52:23 ppmpbx dhcpd: DHCPDISCOVER from 00:0b:82:70:f7:41 via eth0
Aug 23 13:52:24 ppmpbx dhcpd: DHCPOFFER on 192.168.71.68 to 00:0b:82:70:f7:41 via eth0
Aug 23 13:52:24 ppmpbx dhcpd: DHCPREQUEST for 192.168.71.68 (192.168.71.30) from 00:0b:82:70:f7:41 via eth0
Aug 23 13:52:24 ppmpbx dhcpd: DHCPACK on 192.168.71.68 to 00:0b:82:70:f7:41 via eth0
Aug 23 13:52:40 ppmpbx in.tftpd[21759]: RRQ from 192.168.71.68 filename /grandstream/1/gxv3275_rescue.bin
Aug 23 13:52:52 ppmpbx in.tftpd[21763]: RRQ from 192.168.71.68 filename cfg000b8270f741
Aug 23 13:52:52 ppmpbx in.tftpd[21764]: RRQ from 192.168.71.68 filename cfg000b8270f741.xml
Aug 23 13:52:52 ppmpbx in.tftpd[21765]: RRQ from 192.168.71.68 filename cfg.xml
Aug 23 13:52:54 ppmpbx in.tftpd[21766]: RRQ from 192.168.71.68 filename /grandstream/1/gxv3275fw.bin

Phones auto reboot after requesting cfg.xml from the TFTP server when there are firmware compatibility, config file errors or provisioning problems.

To troubleshoot, you can manually edit the config file in a 'divide and conquer' method:

1. Make a backup of the problem file
2. Delete half of the file
3. Try it again