How can I load the mobile versions of websites?

By default, 3D WebView uses a User-Agent header that identifies it as a desktop browser. However, if you want to load the mobile versions of websites, you can opt into using a mobile User-Agent with Web.SetUserAgent(), like this:

void Start() {
  // Call this at the start of your application
  // before any webviews are initialized.
  // Now webviews can be initialized...

If you use this approach and it still seems like the mobile version of a site isn't being used, it's likely that the site is styling itself like a desktop site because the width of the webview is significantly wider than that of a phone. For more information on scaling web content to make it appear smaller, please see this article.