Call me maybe

index.html

<ul id="user-list" data-token="eyJ0...">
  <li>
    Pablo Cantero - <a href="#" rel="phone-number">+551199...</a>
   </li>
</ul>

index.html.erb

<script src="//static.twilio.com/libs/twiliojs/1.1/twilio.min.js"></script>

<ul id="user-list" data-token="<%= token %>">
<% @users.each do |user| %>
  <li>
    <%= user.name %> - <a href="#" rel="phone-number"><%= user.name %></a>
  </li>
<% end %>
</ul>

users.js

$(function(){
  Twilio.Device.setup($("#user-list").data("token"));

  $("a[rel=phone-number]").on("click", function(e){
    e.preventDefault();
    
    if(Twilio.Device.status() !== "ready"){
      Twilio.Device.disconnectAll();
      return;
    }
    
    $this = $(e.target);
    Twilio.Device.connect($this.text());
  });
});

users.js.coffee

$ ->
  Twilio.Device.setup $("#user-list").data "token"

  $("a[rel=phone-number]").on "click", (e) ->
    e.preventDefault()
    
    if Twilio.Device.status() != "ready"
      Twilio.Device.disconnectAll()
      return
    
    $this = $ e.target
    Twilio.Device.connect $this.text()

users_controller.rb

# Gemfile: gem "twilio-ruby"

class UsersController < ApplicationController
  def index
    account_sid = ENV["TWILIO_ACCOUNT_SID"]
    auth_token = ENV["TWILIO_AUTH_TOKEN"]
    twiml_app_sid = ENV["TWILIO_TWIML_APP"]

    capability = Twilio::Util::Capability.new account_sid, auth_token
    capability.allow_client_outgoing twiml_app_sid

    @token = capability.generate

    @users = User.all
  end
end