Kol Isha followup

Question

It is clear from your answer to the prior post that for a woman to SING in public is obviously forbidden....but what about a woman delivering a D'var Torah, a speech, and/or making personal prayers (spoken, not sung) from the Bima, on Shabbat morning either just before or after the Torah reading? I have seen this and always thought it too was forbidden. Is this forbidden or permitted?