Rainbow Office Embeddable is an all-in-one widget that can be installed in any web app with just a few lines of code.
Rainbow Office Embeddable enables developers to quickly embed voice and text into their web applications. With Rainbow Office Embeddable, you can embed a full-featured softphone into your favorite web application for an integrated communications experience that drives productivity and ease of use without lengthy development time.
Must be a Rainbow Office customer- supported for any tier.
Please reference https://developer.ringcentral.com/embeddable-voice.html for install details.