There is a Speak script step in the Miscellaneous section.
Yep! It only works on Mac, not on iOS (FMGo: iPhone/iPad) <http://help.filemaker.com/app/answers/detail/a_id/7734/~/calculation-and-scripting-behavioral-differences-in-filemaker-go>. Although the help topic only says it won't work on Web Publishing or Scheduled scripts on Server: <http://www.filemaker.com/help/html/scripts_ref2.37.58.html#1029432> And, of course, it doesn't work on Windows. Your choices are limited...
Here's a good article on the script step: <http://www.dwaynewright.com/scripting/2008/8/28/filemaker-the-speak-script-step-macintosh-only.html>
Doh! I can't believe I missed it! I ended up doing it in Applescript instead. Many thanks ...