SIPGetHeader( ) Gets a SIP header from an incoming SIP call
SIPGetHeader(var=headername)
Sets a channel variable named var to the content of the headername SIP header. Skips to priority n+101 (where n is the current priority) if the specified header does not exist.
; get the "To" header and assign it to the variable called TESTING
exten => 123,1,SIPGetHeader(TESTING=To)