Webmentions are a way to send in your comments and other such likes, no SMS or registration required.
Thing is, you don’t leave your comment on my site, you do it elsewhere. I get a notification, and a simple server-side app asks the aggregator (webmention.io in my case) for the comments, saves them to my site, and shows them to you. If you feel the need to change or delete a comment, the best way is to change or delete it wherever you’ve published it, and my site will reflect the change (though not immediately, perhaps).