I believe that's a mac only feature. Since I have windows, I can't test this, but see if Go to field with the select contents option selected can be used to bring up the controls for recording sound into the container field. (You'd still have to click a button in the controls to start recoring, however.)
Can you check my other question about tabbed layouts, if you have a minute?
I had one more question there...
I believe I've answered them unless you've posted a second follow up question.
PhilModJunk's answer works.
But if you are using this in Filemaker Go on Ipad or Ipod or Iphone, it doesn't support recording sound. A dialog box pop's up instead asking if you want to take a picture.