The network effect of mass messaging was tested at smaller scales many times. Victorian era pneumatic tubes come to mind or unlimited local calls later, but there must be countless other examples that did not require changing the economy as a whole.

but is changing the economy as a whole a fair characterization of UBI?

That’s a disservice to the existing complexity of modern economies.

Valid arguments not downvoted pls

I think the overwhelming majority of transactions can be characterized as a trade (of goods for money, services for money, work for money, money for other money (in form or time), etc.)

UBI seems quite different in that regard and, while it doesn’t invalidate everything, it introduces a lot more of money for nothing and a corresponding nothing for money trade that is required to fund it.