You don't. Each pigeon goes to one place, the place that is "home" for that pigeon. So, you keep the pigeon with you so you can send a thing or a message to one particular place where the pigeon is from and to which it will go "home" when you release it, and it won't come back. You COULD set up a two way system where "home" is where you are for pigeons you gave your friend and "home" is your friend's house for pigeons you gave him. But every so often someone would have to bring the pigeons back manually. That's pretty much all there is to it. Obviously not as useful of a system as you apparently thought.