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.
In an effort to woo developers to build features for Google Assistant, the search giant's virtual personal assistant offering, Google this week announced a number of new functionality that is available or will be coming to its Google Assistant platform. This includes a new push notification API.
CallME's RESTful click-to-call API allows you to integrate Click-to-Call into your website as connect any phone number to another number easily. The service provides calling from a browser, voice messaging and a few other telephony features.