The MeaningCloud Text Classification PHP Sample Code demonstrates how to access the API to implement text classification features into applications and websites.
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's communication APIs are behind the communications of many recognisable brands, including Uber, Salesforce, and AWS. In this tutorial on the Twilio Blog, Sam Agnew provides everything you need to validate phone numbers in Node/JavaScript using the Twilio Lookup API as a REST API phonebook.
A little less than a year after launching a private beta of the UK government's notification platform, GDS has upgraded to v2 of the associated API. GOV.UK Notify is a service that allows the government to text, email, and send letters to citizens and track the progress of such notifications.