I'm pretty impressed with Microsoft's System.Speech API. It took less than 3 days to throw together a proof-of-concept application. The hardest part was probably coming up with the grammar -- documentation for that is pretty thin on the ground. Anyways, here's the application source code on GitHub if anyone wants a look: ObserverLengthSampler project If nothing else, I'd recommend it as a starting point for someone needing a number recognition SRGS grammar in an XML format.