xAuth is still supported for apps that have access to it, though if you’re on iOS you really owe it to yourself and our users to use the more user-informative web-based OAuth flow instead.
If you’re seeing HTTP 404 or HTTP 410 codes, it’s likely not an issue with using xAuth itself but instead what you do after obtaining a token – any API calls you make to api.twitter.com/1/* need to move to API v1.1 equivalents. Review the docs on this site to understand further.