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$caller$ - caller ID
$caller_name$ - caller name
$number$ - called number (extension)
$called$ - original called number
[sip.Header-Name] - pass any non-RFC3261 SIP header value
Example: https://example.com?to=$number$&called=$called$&calling=$caller$&name=$caller_name$&subj=[sip.X-Subject]
Specifying custom parameters in the webpages or screen pop-up URLs
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