nit: I'd rather return early instead of indenting the `if` statement contents:

```js
    render: function() {
      if (!this.appStatus.get('workerInitialized')) 
        return this;  
      if (!this.user.get('username')) {
        // SPA is initialized but user is not connected.
        this.$el.hide();
      } else {
        // The user is connected to the SPA.
        if(this.spa.supports('pstn-call')) {
          this.$('#dialin-tab').show();
        } else {
          this.$('#dialin-tab').hide();
        }
        this.usersView.render();
        this.dialInView.render();
        this.gearMenuView.render();
        this.importContactsView.render();
        this.$el.show();
      }
    }
```