Oh, a Ubird is kind of like a flying taxi service they have here!! It's like this cable-car like thing held in the claws of a biiig bird! I think they've called Corviknight? Or other large and strong bird-types.

[Ochako's sure she saw a Braviary carrying one of the taxis a long time ago.]

But you can pay a fee to have one of them fly you to different places. Obviously the farther from where you are, the more expensive...and I don't think they can take you outside the region you're in. For example, if you want to get from, Um...Azalea town to I think it was...Cerulean? Yeah, that. You'd have to take a Ubird to Goldenrod, take the rail-line there to wherever it leads to in Kanto, then take another Ubird to get to Cerulean.

That's why it's so handy to have a Pokemon that can just Fly anywhere.