I would like to share another option to send SMS trough a COM port. Here (http://palkotools.wordpress.com/2011/06/01/smssender-en/) you can download a executable.
Simply create a new notification using EXE, point to SMSSender.exe.
In the parameters we use:
-p:COM3 -d:+31612345678 -t:int -msg:"%device %name %status %down (%message)"
Note that you can use the variables as PRTG describes.
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