Maybe this is a stupid question, because there are libraries for native android and ios devices, but what about the JavaScript library? Does it work on browsers from mobile devices? I made some test with my app, and it doesn't work.
I see on Can I use that WebRTC right now it works only on Firefox, Chrome, Opera, Android Browser and Chrome for Android.
Is WebRTC only for video/audio or for messages also? I am asking this because on the sinch website you have different products for INSTANT MESSAGE and WEBRTC.
WebRTC can theoretically be used for messaging as well, via its data channel, but you still need signaling to be done elsewhere to get the two browsers connected first. The data channel has a lot of additional uses as well such as passing session context (see https://bloggeek.me/webrtc-data-channel-context/)
WebRTC isn't supported natively on iOS, and to date, there's no popular browser that enables you to use JavaScript for it. You can port WebRTC to iOS and use it inside your own iOS app.
On Android, from version 5, you can access WebRTC via a webview inside an app. You can also access WebRTC from the browsers you mentioned (Chrome and Firefox on Android support WebRTC).
There are those who built Cordova plugins for WebRTC to run on Android and iOS. Some open sourced while other commercial.