It's not the same. You cannot transport voice over a pigeon, at least not instantly.
If you don' allow substitutes then every brand has a monopoly on the products of their brand. Technically that's a monopoly. But nobody complains about McDonalds having a monopoly on McDonalds burgers.
And you can't farm without farmland. Selling other goods and services is a very imperfect substitute for farming. Other burgers are a pretty good substitute for McDonald's burgers.
