In general, God used messengers to speak to humans. Examples would be when Gabriel spoke to Mary, “During Elizabeth’s sixth month of pregnancy, God sent the angel Gabriel to Nazareth, a town in Galilee, to a virgin” (Luke 1:26, 27), and also spoke to Zecharias, “While he was in the temple of the Lord, Zacharias was visited by the angel Gabriel: But the angel said to him: ‘Do not be afraid, Zechariah; your prayer has been heard. Your wife Elizabeth will bear you a son,’” (Luke 1:13).
In Exodus 33:19-22 (NIV), God told Moses no one could see God and live, “And the LORD said, ‘I will cause all my goodness to pass in front of you…but you cannot see my face, for no one may see me and live.’ Then the LORD said, ‘There is a place near me where you may stand on a rock. When my glory passes by, I will put you in a cleft in the rock and cover you with my hand until I have passed by.’” Moses’ close communion with God was evidenced by his glowing face. (See Exodus 34:29-35.)
God, also, used angels to represent Himself when He communicated with Abraham. Genesis 18:1-3 (NIV), “The LORD (Jehovah) appeared to Abraham near the great trees of Mamre while he was sitting at the entrance to his tent in the heat of the day. Abraham looked up and saw three men standing nearby…(he) bowed low to the ground. He said…my lord…” Abraham bowed down to them and addressed them as Lord; however, he obviously know they weren’t God Himself.
At another time, God sent the angel Gabriel to deliver a message to Daniel. Daniel 8:16, “And I heard a man's voice between the banks of Ulai, which called, and said, Gabriel, make this man to understand the vision.”
Thus, we may conclude that in general, messengers, i.e., angels, would speak on God’s behalf. We can’t be dogmatic about this as there are no direct Scriptures that say so. But this reasoning appeals to us.