Finally a voice stammered slowly and awkwardly: "S-s-ssir...?"

Jamie's voice was unsteady, tripping and stammering from time to time.

He was rather proud that his voice neither stammered nor had a trace of tremor.

The face and ears of young Jeremy Redthorn ought to have been turning red; his voice should have been stammering.

Excitedly, the voice stammered, "C-can't you dig?

"Well," the voice stammered, "you charged me late fees when I was only late once in 10 years, and then you all were rude to me on the phone."

Even her inner voice was stammering!

The voice stammers in a high register, on the edge of ululation, and is sliced or chopped off by an instrumental action.

I h-hear," the voice stammered as a series of clanks and chatterings: announced the opening of the hatch.

"Another sh-ship, Prefect," the voice stammered.