It also assures both that if something comes up, one can contact the other.
Now, saying that, if I give my number to a woman and she is constantly calling or texting me, I feel that I have a potential stalker and/or someone that has this need to check up on another.
The phone is purely improvisation based on different environments, if someone tries to control it then it comes off really bad.
I see chatting with someone on the phone before even meeting them the same as if I were to randomly call someone in India.
EDIT: below, I prefer to meet a person live if they are close by, if that isnt available then the phone. I know there is a lot of apprehension and nervousness. Especially on the phone since someone is basically just sitting there staring at a wall trying to come up with something to say rather than spout on about how nervous they are.