Flash MX 2004.
frame.name
Property; a string that specifies the name of the frame.
The following example sets the name of the first frame, top layer to "First Frame" and then stores the name value in the frameLabel variable:
fl.getDocumentDOM().getTimeline().layers[0].frames[0].name = 'First Frame';
var frameLabel = fl.getDocumentDOM().getTimeline().layers[0].frames[0].name;