Our API directory now includes 73 voice APIs. The newest is the Ivona API. The most popular, in terms of mashups, is the Twilio API. We list 340 Twilio mashups. Below you'll find some more stats from the directory, including the entire list of voice APIs.
Ask Ziggy, best known as the "Siri for Window's Phone," has launched the Ask Ziggy API, which enables natural speech processing within any app. The API enables speech processing, but must be used in conjunction with other speech services to complete the offering (e.g. Nuance, AT&T, etc.). Ask Ziggy expects the API to be used primarily for enhanced in-app search features; however, the opportunities extend much further than basic search.