An HTTP GET request can contain variable name and variable value, separated by "=".  Each variable value starts with a "$" in the query part of the URL.
The valid URL format is: http(s)://<IPADDRESSorFQDN>/Script.xml?VariableName=$VariableValue.
Variable name can be customized by users, while the variable value is pre-defined. For example, a URL http://172.16.0.1/script.xml?mac=$mac is specified for the event Mute, $mac will be dynamically replaced with the MAC address of the ClearlyIP Phone when the ClearlyIP Phone mutes a call. 

Variable	Description
$mac	MAC address of the ClearlyIP Phone
$ip	The current IP address of the ClearlyIP Phone
$model	Phone model
$firmware	Phone firmware version
$active_url	The SIP URI of the current account when the ClearlyIP Phone places a call, receives an incoming call or establishes a call.
$active_user	The user part of the SIP URI for the current account when the ClearlyIP Phone places a call,receives an incoming call or establishes a call.
$active_host	The host part of the SIP URI for the current account when the ClearlyIP Phone places a call, receives an incoming call or establishes a call.
$local	The SIP URI of the caller when the ClearlyIP Phone places a call. The SIP URI of the callee when the ClearlyIP Phone receives an incoming call.
$remote	The SIP URI of the callee when the ClearlyIP Phone places a call. The SIP URI of the caller when the ClearlyIP Phone receives an incoming call.
$display_local	The display name of the caller when the ClearlyIP Phone places a call. The display name of the callee when the ClearlyIP Phone receives an incoming call.
$display_remote	The display name of the callee when the ClearlyIP Phone places a call. The display name of the caller when the ClearlyIP Phone receives an incoming call.
$call_id	The caller ID of the active call.