The MindMeld iOS SDK by Expect Labs is a set of development tools that enable developers to add voice-driven search to their iOS application. The most important functionality of this SDK is found in the MMApp Object, as most calls and requests are made from here.
If it's speech-to-text services you're after, Vocapia Research is in the game, offering a variety of speech technology services and working with their clients to adapt, fine tune or create products that are relevant for specific applications. One of Vocapia's products is the VoxSigma speech-to-text software suite that is suitable for many languages and a variety of audio data types. The VoxSigma API is available as a Web service via a REST API over HTTPS.