Take it from one of my best pickup instructors 8, it means SO MUCH more to talk to someone on the phone ESP if they like you enough to give you their number.
According to personal experience, starting a long text thread with them is a sure fire way to FLAKEage.
I always avoid texting, or even talking to ANY ToI over the phone for any reason other than MAKING A DATE! Prove to her that your time is precious to you and you have better things to do.
After all, there are really two types of men in this world, busy men and boring men! I bet I can't guess which one YOU want to be! xD