What changes once there is a booking

The moment a booking closes on the listing, the restriction on contact details in that conversation is lifted.

Both sides can then send a phone number, a link or whatever the arrangement needs. There is nothing left to withhold: the details have opened anyway.

Along with it, the street, the house number, the internal location and the other party's phone number are released.

A conversation without a booking stays restricted, even if you wrote in it that you had agreed. What lifts the restriction is a booking, not agreement in text.