I've been playing around with this and have achieved it by creating a VBScript that updates the XML file located @ %appdata%\3CXPhone for Windows\3cxphone.xml
Create a GPO that runs a simple VB file at logon and I can now control client side 3cx settings across my network.
In case anyone is interested, here is my VBscript code -
Set FSO = CreateObject("Scripting.FileSystemObject")
Set objWShell = WScript.CreateObject("WScript.Shell")
Set xmlDoc = CreateObject("Microsoft.XMLDOM")
appData = objWShell.expandEnvironmentStrings("%APPDATA%")
if fso.fileexists(appData & "\3CXPhone for Windows\3cxphone.xml") then
xmlDoc.Async = "False"
xmlDoc.Load(appData & "\3CXPhone for Windows\3cxphone.xml")
set node = xmlDoc.selectsinglenode ("//Accounts/Profiles/Profile/UseIdleStatus")
node.text = "True"
xmldoc.save(appData & "\3CXPhone for Windows\3cxphone.xml")
end if