Point your browser to http://servername/ShorewareResources/ClientInstall to find the download link for the ShoreTel Communicator.

In an Administrator command prompt, run Setup.exe /b”C:\extracted”  (note there is intentionally not a colon after /b)

The GUI installer will decompress the .msi and 1033.mst files to the path specified, and present you with Next or Cancel. Choose Cancel and then Finish. (1033.MST is just an English language transform that is not really needed.)

You now have your files extracted from the Installshield exe so that you can use to deploy ShoreTel Communicator via a Group Policy Object. (GPO)

Unfortunately running Setup.exe /? will not help you. I found the /b in an Installshield manual. The files are also extracted to a GUID named folder in %temp% too, but this is a safer bet.