In America we like to call people by their name, not their title, especially for a service role. Otherwise it comes off as very classist and elitist. Someone calling out "Waiter!" would come off as a bit of an asshole, to be honest.
I’m terrible with names, though.
But if they are busy, then I'll do an "Excuse me" really nicely and just loud enough so they can hear - not too loudly, and they will nod and that usually is it, and I know it to mean that they will get to me as soon as they can, they acknowledged me. And if it is super busy, I'm cool if it takes a little longer than usual. It happens. If I'm in a hurry, I'd go to McDonalds. Not really, I hate it, but that's the idea.
In Argentina I revert to "chico"/"chica" but ...is that offensive? Hah.
You want to use standard and customary forms of communcation, though. You can be a little friendlier, or a little more formal, but it's never good to stray too far if meeting or talking to a person the first time.
However, if you get a bead on the person and their personality, you can adjust your style to theirs is best.