Genuinely hard to do. Even if we ignore the problem of guns in the US (this also happens in the europe, for example).

Emergency services kind of have to assume every call is real and act accordingly. In hostage and shooting situations there’s not really much time to debate the validity of the case, because if they delay and it was a real situation, they now are responsible for potentially more victims.

The only real solution is that the forces need to arrive with the potential that it’s a fake call. But that’s easier said than done

Oh, and prosecute the hell out of the callers. Which is not always possible, depending how energy they put into making the call anonymous