The Flowroute Messaging PHP SDK by Flowroute offers integration with a VoIP and messaging platform designed for PHP applications. This SDK supports the v2 APIs from Flowroute that provides outbound SMS with its Messaging API. It requires PHP 5.4.0+.
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.