You need to have a strong marketing plan in any marketing promotion or launch to make it successful. You will create a demand and urgency to order your product by using the "reason why" approach.
That's not a good "reason why" tactic in my humble opinion. Will you agree that if you have a lot of prospects who want to get on your call, it's not possible to increase the lines for more participants? That may be valid. Who knows, they really will not be able to extend more lines.