Nexmo offers a series of cloud-based communication APIs that make it easy to integrate reliable communication services into any application. This tutorial by Tim Lytle on the Nexmo blog shows followers how to build a simple text message group chat using the Nexmo SMS API and PHP.
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.
Twilio has launched the Message Feedback API which monitors when end users receive messages. The API tracks actions that indicate when a message was received and reports the action back to Twilio. In turn, Twilio can tweak its services and delivery to adjust for network variances across the globe.