I've wondered the same about switching the to address and return address but not including a stamp. They go to "return" let letter and end up delivering it, unless postage is checked at time of pickup.
I was the first in my my friend group in highschool to have a car and a cell phone. My friends would call my cell collect from a payphone and just say where they wanted me to meet them. Never needed a name or explanation, if I got a collect call with a location I would decline it and be there as soon as I could.