1)
What is the significance of "v'Hayah Terem Yikra'u va'Ani E'eneh..."?
1.
Radak: This is the opposite of in Galus, "Sakosa ve'Anan Lach me'Avor Tefilah" (Eichah 3:44).
2.
Malbim: This explains why they will not need to scream at all.
2)
Why does it say "before they call" and "while they are speaking"?
1.
Radak: Sometimes He will answer before they call, and sometimes while they are speaking.
2.
Malbim: "Before they call" is what they intended to pray for. "While they are speaking" refers to discussing their needs among themselves - "Ani Eshma", and I will fulfill their hearts' desires before they call.