This document enumerates all those XML tags added/removed/changed between various firmware versions.
It is based on spacfg.xml saved from SPA504G phone with factory-default configuration.
MAC addresses, serial numbers and IP adresses has been removed from file.
Note the 7.3.7 spacfg.xml file contain configuration for all Ext_1 ... Ext_12 regardless of number of extensions supported on particular device. Newer version contain only those Ext_N sections valid for device in question.