From Sheikh Yusuf Al-Qaradawi's response to a question regarding a woman's voice, in Islam:
The promotion of such negativity against women has led many 'scholars' and 'Imams' to make the unsubstantiated ruling about female speech. They claim that women should lower their voice to whispers or even silence except when she speaks to her husband, her guardian or other females. The female act of communication has become to some a source of temptation and allurement to the male.
The Qur'an, however, specifically mentions that those seeking information from the Prophet's wives were to address them from behind a screen (Al-Ahzab 33: 53). Since questions require answers, the Mothers of the Believers offered fatwas to those who asked and narrated hadiths to whomever wished to transmit them.
Furthermore, women were accustomed to posing questions to the Prophet (peace and blessings be upon him) while men were present. Neither were they embarrassed to have their voices heard nor did the Prophet (peace and blessings be upon him) prevent them from forwarding their inquires. Even in the case of `Umar when he was challenged by a woman during his khutbah (Friday sermon) on the pulpit, he did not deny her. Rather, he admitted that she was right and he was wrong and said: 'Everybody is more knowledgeable than `Umar.'
Another Qur'anic example of a woman speaking publicly is that the daughters of the Shu`ayb mentioned in the Qur'an in surat Al-Qasas, verse 23. Furthermore, the Qur'an narrates the conversation between Sulayman and the Queen of Sheba as well as between her and her subjects.
All of these examples support the fatwa that women are allowed to voice their opinion publicly, for whatever has been prescribed to those before us is prescribed to us, unless it’s unanimously rejected by Islamic law.
Read on at: Islam Online