Yes there is.  There is a field called “lap counter” in the Viking IP programming application (on the “phone settings” tab).  When this field is set to “disabled” (it is by default), it will keep calling until it gets answered.  You have the option to set the lap counter to “1” to “9”.  This is the number of times it will call the list of programmed phone numbers before it hangs up, when the call doesn’t get answered because of ring no answer or busy.  Set it to one if you only want it to make one call to extension 300 and then hang up if not answered within a few rings (7 by default).