Name
SetGlobalVar() — Sets a global variable to the specified value
Synopsis
SetGlobalVar(n=value)
Note
This application has been deprecated in favor of:
Set(GLOBAL(var)=...)
Sets a global variable called n to the
      specified value. Global variables are
      available across channels.
; set the NUMRINGS global variable to 3
exten => 123,1,SetGlobalVar(NUMRINGS=3)