(creator of DTMF.io here) I don't see WebRTC as being too much of a hurdle. If the user is running recent-ish Chrome or Firefox, they don't need to know about

(creator of DTMF.io here) I don't see WebRTC as being too much of a hurdle. If the user is running recent-ish Chrome or Firefox, they don't need to know about WebRTC any more than you need to know about HTTP in order to load the website. It just happens to be the technology we use to make the voice calls work: you still type a number into a box and click a button and then talk. If they're running Safari, they're unfortunately completely out of luck for now - but SMS will still work!