Building a call app Using WebRTC, best approach?

I am planning to build a web app, to allow anyone to make calls. The idea is very simple:

Anyone can login into the platform by signing in with their phone numbers. Then they will receive a SMS with a code which they will need to enter to login. After they have logged in, they can start making calls using the web platform. When they call, their number will be used to make the call. They can call anyone regardless of if they are using the web app or not.

I assume it will be a combination of: Twilio - to get SMS authentication WebRTC - to get the call function JS/Ruby on Rails - framework

Am I missing anything?