Is the Talbiyah a pillar of Ihram or a Sunnah?

Scholarly opinions vary regarding the ruling on the Talbiyah for Hajj and Umrah. Some scholars consider it a confirmed Sunnah, others deem it obligatory, incurring a compensatory sacrifice (dam) if neglected. Some consider it obligatory but replaceable by another form of remembrance, while others consider it a pillar without which the ihram is not valid. Ibn Baz and Ibn Uthaymeen held the view that it is a confirmed Sunnah for both men and women, and it is sunnah for a man to raise his voice with it, but not for a woman.