It's good to have a few #s handy as there's always a chance they'll be busy with airport transfers. I've used Damion James for local rides. He's Kingsley's son, very good person and reasonably priced.
I agree Melody, obviously it's not reasonable to expect one person to be on hot stand-by waiting for a single customer. I hope to arrive at the airport with one "main" guy as well as a couple back-ups.